mock/tests: add method Helper() to all mock of *testing.T

mock/mock_test.go

@@ -121,6 +121,9 @@ type MockTestingT struct {
 	logfCount, errorfCount, failNowCount int
 }
 
+// Helper is like [testing.T.Helper] but does nothing.
+func (MockTestingT) Helper() {}
+
 const mockTestingTFailNowCalled = "FailNow was called"
 
 func (m *MockTestingT) Logf(string, ...interface{}) {