Fix PIE installation to use commit SHA instead of branch name

- Use ${{ github.sha }} instead of branch reference
- Prevents git checkout failures when branch history is rewritten
- Ensures PIE can reliably checkout the specific commit

Signed-off-by: James Duong <[email protected]>

Author: jduo

.github/workflows/test-pie.yml

@@ -86,7 +86,7 @@ jobs:
                   "source": {
                     "type": "git",
                     "url": "https://github.com/jduo/valkey-glide-php.git",
-                    "reference": "${{ github.head_ref || github.ref_name }}"
+                    "reference": "${{ github.sha }}"
                   },
                   "type": "php-ext",
                   "php-ext": {