microbench-ci: fix err check panic

The `skipPermissionError` function should be able to handle nil errors,
otherwise we panic when trying to string match on a specific error.

Epic: None
Release note: None

Author: herkolategan

pkg/cmd/microbench-ci/main.go

@@ -164,6 +164,9 @@ func makeCompareCommand() *cobra.Command {
 			}
 			if hasLabel || suite.changeDetected() {
 				skipPermissionError := func(err error, action string) error {
+					if err == nil {
+						return nil
+					}
 					// If this is a permission error, we don't want to fail the build. This
 					// can happen if the GitHub token has read-only access, for example when
 					// testing the pull_request trigger from a fork.