CI: Force invalidate macOS cache

I *hate* having to commit this kind of noise to our
commit history. Especially on a Friday at 10 pm.

.github/workflows/macos_builds.yml

@@ -4,7 +4,7 @@ on: [push, pull_request]
 # Global Settings
 env:
   # Only used for the cache key. Increment version to force clean build.
-  GODOT_BASE_BRANCH: master-v2
+  GODOT_BASE_BRANCH: master-v3
   SCONSFLAGS: verbose=yes warnings=extra werror=yes module_text_server_fb_enabled=yes
 
 concurrency: