README: Pin GitHub Actions with commit SHA using pinact

Author: haya14busa

README.md

@@ -101,13 +101,13 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
-        uses: actions/checkout@v4
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Set up Ruby
-        uses: ruby/setup-ruby@v1
+        uses: ruby/setup-ruby@1a615958ad9d422dd932dc1d5823942ee002799f # v1.227.0
         with:
           ruby-version: 3.0.3
       - name: brakeman
-        uses: reviewdog/action-brakeman@v2
+        uses: reviewdog/action-brakeman@5083efd49634e26645a0736681b618ccc3fb7f14 # v2.19.2
         with:
           brakeman_version: 4.8.2
           reporter: github-pr-review # Default is github-pr-check