[3.12] gh-127359: Pin Tcl/Tk to 8 (8.6) for testing macOS (GH-127365) (#127394)

Author: hugovk

.github/workflows/reusable-macos.yml

@@ -36,7 +36,10 @@ jobs:
         path: config.cache
         key: ${{ github.job }}-${{ inputs.os }}-${{ env.IMAGE_VERSION }}-${{ inputs.config_hash }}
     - name: Install Homebrew dependencies
-      run: brew install pkg-config [email protected] xz gdbm tcl-tk
+      run: |
+        brew install pkg-config [email protected] xz gdbm tcl-tk@8
+        # Because alternate versions are not symlinked into place by default:
+        brew link tcl-tk@8
     - name: Configure CPython
       run: |
         GDBM_CFLAGS="-I$(brew --prefix gdbm)/include" \