Update actions/checkout action to v2 (#363)

Co-authored-by: Renovate Bot <[email protected]>

Author: renovate[bot]

.github/workflows/lsif.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-latest
     container: sourcegraph/lsif-go
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f # renovate: tag=v2
       - name: Generate LSIF data
         run: lsif-go
       - name: Upload LSIF data