Add unshallow to CI

Author: Denis Krivak

.github/workflows/pr.yml

@@ -48,6 +48,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
+      - name: Unshallow
+        run: git fetch --prune --unshallow
       - name: Install Go
         uses: actions/setup-go@v1
         with: