Merge pull request #762 from ruby/dependabot/github_actions/step-security/harden-runner-2.21.0

Bump step-security/harden-runner from 2.20.1 to 2.21.0

Author: matzbot

.github/workflows/push_gem.yml

@@ -23,7 +23,7 @@ jobs:
 
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@b09bb98e06d4d774595224525879c09bc6e98c40 # v2.20.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit