Apply suggestions from code review

Co-authored-by: Justus Magin <keewis@users.noreply.github.com>

Author: jsignell

doc/whats-new.rst

@@ -36,7 +36,7 @@ Breaking changes
 Deprecations
 ~~~~~~~~~~~~
 
-- Start deprecation cycle for changing the default keyword arguments to ``concat``, ``merge``, ``combine``, ``open_mfdataset``.
+- Start a deprecation cycle for changing the default keyword arguments to ``concat``, ``merge``, ``combine``, ``open_mfdataset``.
   Emits a ``FutureWarning`` when using old defaults and new defaults would result in different behavior.
   Adds an option: ``use_new_combine_kwarg_defaults`` to opt in to new defaults immediately.
 

xarray/structure/alignment.py

@@ -456,7 +456,7 @@ def update_dicts(
                     ):
                         emit_user_level_warning(
                             self.join.warning_message(
-                                "This change will result in the following ValueError:"
+                                "This change will result in the following ValueError: "
                                 "cannot be aligned with join='exact' because "
                                 "index/labels/sizes are not equal along "
                                 "these coordinates (dimensions): "