[master] Update GitHub Actions (#322)

Copied from `https://github.com/knative/.github/tree/master/workflow-templates`.
/assign n3wscott vagababov
/cc n3wscott vagababov

.github/workflows/knative-go-build.yaml

@@ -41,8 +41,6 @@ jobs:
 
       - name: Check out code
         uses: actions/checkout@v2
-        with:
-          fetch-depth: 1
 
       - name: Vet
         run: go vet ./...

.github/workflows/knative-go-test.yaml

@@ -41,8 +41,6 @@ jobs:
 
       - name: Check out code
         uses: actions/checkout@v2
-        with:
-          fetch-depth: 1
 
       - name: Test
         run: go test -race ./...

.github/workflows/knative-style.yaml

@@ -36,8 +36,6 @@ jobs:
 
       - name: Check out code
         uses: actions/checkout@v2
-        with:
-          fetch-depth: 1
 
       # TODO: add prettier step
       # TODO: add goimports step

.github/workflows/knative-verify.yaml

@@ -50,7 +50,6 @@ jobs:
     - name: Check out code onto GOPATH
       uses: actions/checkout@v2
       with:
-        fetch-depth: 1
         path: ./src/knative.dev/${{ github.event.repository.name }}
 
     - name: Update Codegen