Permissions and IsExecutableBy in File Existence Tests contradictory

I would have opened a PR for this but I'm not going through legal CLA stuff for changes like this, so here comes an issue instead.

In the example at https://github.com/GoogleContainerTools/container-structure-test?tab=readme-ov-file#file-existence-tests the Permissions and the IsExecutableBy:group contradict each other - the latter requires the file to be executable by the group, but the former requires that the group does not have the executable bit set on the file.