CI (macos): Work around conflict between pre-installed and Homebrew P…

…ython.

Force overwriting files from the pre-installed version of Python. They
conflict with the files from Homebrew's versions of Python.

.github/workflows/build-macos-homebrew.yaml

@@ -35,10 +35,18 @@ jobs:
         uses: actions/checkout@v4
 
       - name: install dependencies
+
+        # Homebrew's Python conflicts with the Python that comes pre-installed
+        # on the GitHub runners. Some of the dependencies depend on different
+        # versions of Homebrew's Python. Enforce using the ones from Homebrew
+        # to avoid errors on updates.
+        # See: https://github.com/orgs/Homebrew/discussions/3928
+
         # It looks like "gfortran" isn't working correctly unless "gcc" is
         # re-installed.
         run: |
           brew update
+          brew install --overwrite [email protected] [email protected]
           brew reinstall gcc
           brew install \
             cmake libomp openblas open-mpi suitesparse \