chore: clean up tests (#37715)

1. use MockVariableValue as much as possible
2. use wg.Go as much as possible instead of Add/Done
3. simplify global lock's DefaultLocker logic to make it easier to test
4. introduce a general approach for getting external service config in
CI
5. remove unclear & unnecessary "t.Skip"
6. use modern generic syntax for remaining "DecodeJSON" calls
7. clarify test result for "list gitignore templates" and "list
licenses"

tests/integration/lfs_view_test.go

@@ -129,8 +129,7 @@ func TestLFSLockView(t *testing.T) {
 		req.Header.Set("Accept", lfs.AcceptHeader)
 		req.Header.Set("Content-Type", lfs.MediaType)
 		resp := session.MakeRequest(t, req, http.StatusCreated)
-		lockResp := &api.LFSLockResponse{}
-		DecodeJSON(t, resp, lockResp)
+		lockResp := DecodeJSON(t, resp, &api.LFSLockResponse{})
 		lockID = lockResp.Lock.ID
 	}
 	defer func() {