Pin coursier/cache-action to SHA1.

Author: yruslan

.github/workflows/scala.yml

@@ -39,7 +39,8 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v6.0.2
-      - uses: coursier/cache-action@v6
+        # gh api repos/coursier/cache-action/commits/v6.4.9 --jq '.sha'
+      - uses: coursier/cache-action@4e2615869d13561d626ed48655e1a39e5b192b3c
       - name: Setup JDK and sbt
         uses: actions/setup-java@v4.2.1
         with: