Fix grammar in error message (#23273)

Fixes the grammar in the error message in case a runner token has
already been activated

routers/api/actions/runner/runner.go

@@ -52,7 +52,7 @@ func (s *Service) Register(
 	}
 
 	if runnerToken.IsActive {
-		return nil, errors.New("runner token has already activated")
+		return nil, errors.New("runner token has already been activated")
 	}
 
 	// create new runner