[gitk] searching commits includes irrelevant file renaming entries

[Lyndon Brown <jnqnfe@xxxxxxxxx>]

Hi,

When searching commits in add/remove string mode, the search results
include commits that simply rename files that contain the string. UX
would be improved IMO if it were to ignore such commits.

I'm a Debian Linux user, running version 1:2.28.0-1.