Add optional go-apidiff test to CI (operator-framework#86)

.github/workflows/ci.yml

@@ -57,3 +57,20 @@ jobs:
       uses: golangci/golangci-lint-action@v2
       with:
         version: v1.35.2
+
+  go-apidiff:
+    name: go-apidiff
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+    - name: Set up Go
+      uses: actions/setup-go@v2
+      with:
+        go-version: ~1.16
+      id: go
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    - name: Run go-apidiff
+      uses: joelanford/go-apidiff@master