CI: Fix macOS build

If Python is installed/updated without "--overwrite",
conflict errors occur because Homebrew tries to replace
existing files like "/usr/local/bin/2to3".

See also:
- actions/runner-images#9966

.github/actions/install-dependencies/install-dependencies.sh

@@ -59,6 +59,10 @@ case "$os" in
     ;;
 
   macos*)
+    # Pre-installed Python conflicts with Homebrew Python
+    # https://github.com/actions/runner-images/issues/9966
+    brew install --overwrite python@3.12
+
     if [ "$build_system" = 'meson' ]; then
       brew install $macos_packages qt@6 meson
     else