chore: adding in region tag for cloud storage v2 unit test docs (#3404)

* refactor: adding in region tag to link back to cloud storage v2 unit test docs

* chore: space clean up

Author: pattishin

functions/v2/helloGCS/test/unit.test.js

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// [START functions_cloudevent_storage_unit_test]
 const {getFunction} = require('@google-cloud/functions-framework/testing');
 
 describe('functions_cloudevent_storage', () => {
@@ -52,3 +53,4 @@ describe('functions_cloudevent_storage', () => {
     assert(console.log.calledWith('File: my-file.txt'));
   });
 });
+// [END functions_cloudevent_storage_unit_test]