Fix HDF5 installation on macOS runners

.github/workflows/testing.yml

@@ -17,7 +17,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [ "3.8", "3.9", "3.10", "3.11", "3.12" ]
+        python-version: ["3.10", "3.11", "3.12" ]
         os: [ ubuntu-latest ]
         include:
           - python-version: "3.12"
@@ -30,7 +30,13 @@ jobs:
 
       - name: Install HDF5 source files
         if: runner.os == 'macOS'
-        run: brew install hdf5
+        # macOS needs special handling for pkg-config/pkgconf conflict
+        # HDF5 depends on pkgconf but homebrew comes with pkg-config pre-installed
+        # We need to unlink pkg-config and force link pkgconf to avoid CI failures
+        run: |
+          brew unlink [email protected] || true
+          brew install hdf5
+          brew link --overwrite pkgconf
 
       - uses: actions/setup-python@v5
         with: