ci: Harden GitHub Actions (#2971)

Signed-off-by: StepSecurity Bot <[email protected]>

Author: step-security-bot

.github/workflows/ci.yml

@@ -220,11 +220,11 @@ jobs:
   build-examples:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: dtolnay/rust-toolchain@4305c38b25d97ef35a8ad1f985ccf2d2242004f2 # stable
         with:
           components: rustfmt
-      - uses: arduino/setup-protoc@v3
+      - uses: arduino/setup-protoc@c65c819552d16ad3c9b72d9dfd5ba5237b9c906b # v3.0.0
         with:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
       - name: Build examples