Pin actions to digests and introduce Step Security Harden Runners (#137)

Signed-off-by: Jed Salazar <[email protected]>

.github/workflows/check.yml

@@ -11,10 +11,14 @@ jobs:
     name: fmt
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - name: Harden Runner
+      uses: step-security/harden-runner@a4aa98b93cab29d9b1101a6143fb8bce00e2eac4 # v2.7.1
+      with:
+        egress-policy: audit
+    - uses: actions/checkout@0ad4b8fadaa221de15dcec353f45205ec38ea70b # v4.1.4
       with:
         submodules: recursive
-    - uses: dtolnay/rust-toolchain@stable
+    - uses: dtolnay/rust-toolchain@d388a4836fcdbde0e50e395dc79a2670ccdef13f # stable
       with:
         components: rustfmt
     - run: ./hack/ci/install-linux-deps.sh
@@ -23,7 +27,11 @@ jobs:
     name: shellcheck
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - name: Harden Runner
+      uses: step-security/harden-runner@a4aa98b93cab29d9b1101a6143fb8bce00e2eac4 # v2.7.1
+      with:
+        egress-policy: audit
+    - uses: actions/checkout@0ad4b8fadaa221de15dcec353f45205ec38ea70b # v4.1.4
       with:
         submodules: recursive
     - run: ./hack/code/shellcheck.sh