Specify Harden-Runner version by commit hash

Author: shugo

.github/workflows/push_gem.yml

@@ -24,7 +24,7 @@ jobs:
     steps:
       # Set up
       - name: Harden Runner
-        uses: step-security/harden-runner@v2
+        uses: step-security/harden-runner@c6295a65d1254861815972266d5933fd6e532bdf # v2.11.1
         with:
           egress-policy: audit