install rattler-build-conda-compat from source for some testing

Author: wolfv

.github/workflows/tests-reusable.yml

@@ -96,6 +96,9 @@ jobs:
 
           python -m pip install -v --no-deps --no-build-isolation -e .
 
+          # also install rattler-build-conda-compat from git source
+          pip install git+https://github.com/prefix-dev/rattler-build-conda-compat@main
+
       - name: start MongoDB
         uses: MongoCamp/mongodb-github-action@e76ad215d47c31a99b4b0b1fde05f6cd1185df1a # e76ad215d47c31a99b4b0b1fde05f6cd1185df1a
         with: