CI: Pin Python 3.12.3 to workaround GHA issue

macOS runners can't extract the 3.12.4 tarball properly it seems.
https://github.com/actions/setup-python/issues/886

.github/actions/godot-deps/action.yml

@@ -3,7 +3,7 @@ description: Setup Python, install the pip version of SCons.
 inputs:
   python-version:
     description: The Python version to use.
-    default: "3.x"
+    default: "3.12.3"
   python-arch:
     description: The Python architecture.
     default: "x64"