gh-37588: Update Conda installation instructions to use Miniforge

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Based on the discussion in https://groups.google.com/g/sage-
devel/c/GaQHdu0Q6UU and #37184, we
now follow the offical recommendation and use Miniforge over the  soft-
deprecated Mambaforge. Since we are exclusively testing on miniforge,
this change also aligns the docs with the ci.

Moreover, I've removed the recommendation to install mamba (using `conda
install mamba`) which is not recommended according to the [offical
docs](https://mamba.readthedocs.io/en/latest/installation/mamba-
installation.html#existing-conda-install-not-recommended).

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- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

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URL: #37588
Reported by: Tobias Diez
Reviewer(s): Matthias Köppe, roed314, William Stein

Author: Release Manager

build/pkgs/configure/checksums.ini

@@ -1,4 +1,4 @@
 tarball=configure-VERSION.tar.gz
-sha1=facd0b123855a68d836680b22177058ac3333aad
-md5=180414ef1a73c5cc12a657abb5affb63
-cksum=101476296
+sha1=ecd112699d45a08acc904081495200200aa5375d
+md5=15351e13c37ab18a3dca25db30f45e33
+cksum=1274317165

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-5c45eed9e45a60223067282bb70cdb805d66eeff
+86e1c3569bfb8b90061cf3aa01801677d0b9cc9e

src/doc/en/installation/conda.rst

@@ -9,32 +9,27 @@ SageMath can be installed on Linux and macOS via Conda from the
 Both the ``x86_64`` (Intel) architecture and the ``arm64``/``aarch64``
 architectures (including Apple Silicon, M1) are supported.
 
-You will need a working Conda installation: either Mambaforge/Miniforge,
+You will need a working Conda installation: either Miniforge (or Mambaforge),
 Miniconda or Anaconda. If you don't have one yet, we recommend installing
-`Mambaforge <https://github.com/conda-forge/miniforge#mambaforge>`_ as
+`Miniforge <https://github.com/conda-forge/miniforge>`_ as
 follows. In a terminal,
 
 .. code-block:: shell
 
-   $ curl -L -O https://github.com/conda-forge/miniforge/releases/latest/download/Mambaforge-$(uname)-$(uname -m).sh
-   $ sh Mambaforge-$(uname)-$(uname -m).sh
+   $ curl -L -O "https://github.com/conda-forge/miniforge/releases/latest/download/Miniforge3-$(uname)-$(uname -m).sh"
+   $ bash Miniforge3-$(uname)-$(uname -m).sh
 
-* Mambaforge and Miniforge use conda-forge as the default channel.
+* Miniforge (and Mambaforge) use conda-forge as the default channel.
 
 * If you are using Miniconda or Anaconda, set it up to use conda-forge:
 
   * Add the conda-forge channel: ``conda config --add channels conda-forge``
 
   * Change channel priority to strict: ``conda config --set channel_priority strict``
 
-Optionally, use `mamba <https://github.com/mamba-org/mamba>`_,
+If you installed Miniforge (or Mambaforge), we recommend to use 
+`mamba <https://mamba.readthedocs.io/en/latest/index.html>`_ in the following, 
 which uses a faster dependency solver than ``conda``.
-If you installed Mambaforge, it is already provided. Otherwise, use
-
-.. code-block:: shell
-
-   $ conda install mamba
-
 
 .. _sec-installation-conda-binary:
 
@@ -43,10 +38,17 @@ Installing all of SageMath from conda (not for development)
 
 Create a new conda environment containing SageMath, either with ``mamba`` or ``conda``:
 
-.. code-block:: shell
+.. tab:: mamba
+
+  .. code-block:: shell
 
-    $ mamba create -n sage sage python=X        # either
-    $ conda create -n sage sage python=X        # or
+      $ mamba create -n sage sage python=X
+
+.. tab:: conda
+
+  .. code-block:: shell
+
+      $ conda create -n sage sage python=X
 
 where ``X`` is version of Python, e.g. ``3.9``.
 
@@ -109,17 +111,22 @@ Here we assume that you are using a git checkout.
 
       $ export SAGE_NUM_THREADS=24
 
-  - As a recommended step, install the ``mamba`` package manager. If
-    you skip this step, replace ``mamba`` by ``conda`` in the
-    following steps::
-
-      $ conda install mamba
-
   - Create and activate a new conda environment with the dependencies of Sage
     and a few additional developer tools::
 
-      $ mamba env create --file src/environment-dev-3.11-linux.yml --name sage-dev
-      $ conda activate sage-dev
+      .. tab:: mamba
+      
+        .. code-block:: shell
+      
+            $ mamba env create --file src/environment-dev-3.11-linux.yml --name sage-dev
+            $ conda activate sage-dev
+      
+      .. tab:: conda
+      
+        .. code-block:: shell
+      
+            $ conda env create --file src/environment-dev-3.11-linux.yml --name sage-dev
+            $ conda activate sage-dev
 
     Alternatively, you can use ``src/environment-3.11-linux.yml`` or
     ``src/environment-optional-3.11-linux.yml``, which will only install standard