gha: pin workflows to hash

.github/workflows/coverage.yml

@@ -19,7 +19,7 @@ jobs:
       LDFLAGS: --coverage
     steps:
       - name: "Checkout ${{ github.ref }} ( ${{ github.sha }} )"
-        uses: actions/checkout@v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           persist-credentials: false
       - name: Ruby version
@@ -39,7 +39,7 @@ jobs:
             echo \`\`\`
           } > "$GITHUB_STEP_SUMMARY"
       - name: Upload coverage report
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: coverage-${{ github.sha }}
           path: coverage/