tell git to ignore file permission changes

I have a project, synchronized with gitlab.  On my local machine, I need to change file permission in order to test it.

However, I don't want file permission changes to be considered as changes. It gave me trouble to see what files that I actually altered and what are not in term of code changes.

How to prevent this issue? How to let git exclude files that only has permission changes?

Here is the command:

git config core.fileMode false