build: Pin GitHub Actions

The main benefit of pinning GitHub actions is the determinism it brings
in terms of what version of a given action will be executed. This is
a step towards having hermetic builds.

Once pinned to a commit, dependabot will automatically issue PRs to update
to newer versions.

Pinned versions is the only security metric from OpenSSF scorecard that
this repository currently have a zero score.

Signed-off-by: Paulo Gomes <paulo.gomes@weave.works>

.github/workflows/scan.yaml

@@ -17,9 +17,9 @@ jobs:
     runs-on: ubuntu-latest
     if: github.actor != 'dependabot[bot]'
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
       - name: Run FOSSA scan and upload build data
-        uses: fossa-contrib/fossa-action@v1
+        uses: fossa-contrib/fossa-action@6cffaa064112e1cf9b5798c6224f9487dc1ec316 # v1
         with:
           # FOSSA Push-Only API Token
           fossa-api-key: 5ee8bf422db1471e0bcf2bcb289185de
@@ -31,21 +31,21 @@ jobs:
       security-events: write
     if: (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository) && github.actor != 'dependabot[bot]'
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
       - name: Setup Kustomize
         uses: fluxcd/pkg//actions/kustomize@main
       - name: Build manifests
         run: |
           make cmd/flux/.manifests.done
       - name: Run Snyk to check for vulnerabilities
-        uses: snyk/actions/golang@master
+        uses: snyk/actions/golang@a8dd587d8a94f5663fa3d67d51abd0cc66aff244 # v0.3.0
         continue-on-error: true
         env:
           SNYK_TOKEN: ${{ secrets.SNYK_TOKEN }}
         with:
           args: --sarif-file-output=snyk.sarif
       - name: Upload result to GitHub Code Scanning
-        uses: github/codeql-action/upload-sarif@v2
+        uses: github/codeql-action/upload-sarif@678fc3afe258fb2e0cdc165ccf77b85719de7b3c # v2
         with:
           sarif_file: snyk.sarif
 
@@ -56,16 +56,16 @@ jobs:
     if: github.actor != 'dependabot[bot]'
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
       - name: Set up Go
-        uses: actions/setup-go@v3
+        uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f
         with:
           go-version: 1.19.x
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@v2
+        uses: github/codeql-action/init@678fc3afe258fb2e0cdc165ccf77b85719de7b3c # v2
         with:
           languages: go
       - name: Autobuild
-        uses: github/codeql-action/autobuild@v2
+        uses: github/codeql-action/autobuild@678fc3afe258fb2e0cdc165ccf77b85719de7b3c # v2
       - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@v2
+        uses: github/codeql-action/analyze@678fc3afe258fb2e0cdc165ccf77b85719de7b3c # v2