ci: pin github actions hashes

Author: mbaraniak-exodus

.github/workflows/ci.yml

@@ -7,8 +7,8 @@ jobs:
     name: Build & Test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-node@v1
+      - uses: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5 # v2.7.0
+      - uses: actions/setup-node@f1f314fca9dfce2769ece7d933488f076716723e # v1.4.6
       - run: npm ci
       - run: npm run build
       - run: npm test