fix: include /opt/homebrew/opt in Homebrew cache paths

The cache restored Cellar, lib, and include but not opt/, where the
symlinks that brew --prefix returns live. Without opt/, the Mesa
libEGL path check fails even though the underlying Cellar files are
present. Also switch to a static cache key (v1) so workflow edits
don't invalidate the cache.

Author: Mearman

.github/workflows/macos-build.yml

@@ -76,9 +76,10 @@ jobs:
         with:
           path: |
             /opt/homebrew/Cellar
+            /opt/homebrew/opt
             /opt/homebrew/lib
             /opt/homebrew/include
-          key: brew-macos-arm64-${{ hashFiles('.github/workflows/macos-build.yml') }}
+          key: brew-macos-arm64-v1
           restore-keys: |
             brew-macos-arm64-