unshallow checkout to always have access to the latest tag during release

.github/workflows/go.yml

@@ -9,6 +9,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
 
     - name: Set up Go
       uses: actions/setup-go@v2