Pin GitHub Actions workflows to a specific version (#677)

Author: ErikSchierboom

.github/workflows/exercises.yml

@@ -12,7 +12,7 @@ jobs:
     name: Rakudo Star on ${{ matrix.os }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
 
       - name: Install Rakudo Star with choco
         if: runner.os == 'Windows'

.github/workflows/generator.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
 
       - run: bin/fetch-configlet
       - run: bin/configlet sync || true