fix(ci): SHA-pin actions/cache (org policy) (#59)

Pins actions/cache@v5 to a full commit SHA; the org policy gate rejects
tag pins, failing the build check.

Author: hyperpolymath

.github/workflows/php.yml

@@ -22,7 +22,7 @@ jobs:
 
     - name: Cache Composer packages
       id: composer-cache
-      uses: actions/cache@v5
+      uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5
       with:
         path: vendor
         key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}