ci/macos: use brew python for unit tests

.github/workflows/macos.yml

@@ -32,10 +32,20 @@ jobs:
     runs-on: macos-latest
     steps:
     - uses: actions/checkout@v4
+    - run: brew update
+    # github actions overwrites brew's python. Force it to reassert itself, by running in a separate step.
+    - name: unbreak python in github actions
+      run: |
+        find /usr/local/bin -lname '*/Library/Frameworks/Python.framework/*' -delete
+        sudo rm -rf /Library/Frameworks/Python.framework/
+        brew install --force python3 && brew unlink python3 && brew unlink python3 && brew link --overwrite python3
+        # Delete nonsensical PEP 668 breakage. It is the wrong solution to the problem and isn't designed to be
+        # productive -- only victim blaming -- however it bites particularly badly because this is a container/VM
+        # See commit 5c479d7a13a518c18ccb4dc3b6bdd7bfc2a9bdb5 for a more thorough analysis.
+        find /opt/homebrew/Cellar/python* -name EXTERNALLY-MANAGED -print0 | xargs -0 rm -vf
     - run: |
-        export PATH="$HOME/Library/Python/3.9/bin:$PATH"
-        /usr/bin/python3 -m pip install --upgrade pip
-        /usr/bin/python3 -m pip install pytest pytest-xdist pytest-subtests fastjsonschema
+        python3 -m pip install --upgrade pip
+        python3 -m pip install pytest pytest-xdist pytest-subtests fastjsonschema
     - run: brew install pkg-config ninja llvm qt@5
     - env:
         CPPFLAGS: "-I/opt/homebrew/include"
@@ -46,9 +56,9 @@ jobs:
         # These cannot evaluate anything, so we cannot set PATH or SDKROOT here
       run: |
         export SDKROOT="$(xcodebuild -version -sdk macosx Path)"
-        export PATH="$HOME/Library/Python/3.9/bin:$HOME/tools:/opt/homebrew/opt/qt@5/bin:/opt/homebrew/opt/llvm/bin:$PATH"
+        export PATH="$HOME/tools:/opt/homebrew/opt/qt@5/bin:/opt/homebrew/opt/llvm/bin:$PATH"
         export PKG_CONFIG_PATH="/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/Current/lib/pkgconfig:/opt/homebrew/opt/qt@5/lib/pkgconfig:$PKG_CONFIG_PATH"
-        /usr/bin/python3 ./run_unittests.py
+        python3 ./run_unittests.py
 
 
   project-tests-appleclang: