As far as I can tell, setting core.safecrlf to false is the only way to turn off that warning.
safecrlf is generally not necessary if your attributes are set correctly. The point of safecrlf is to prevent normalization in a file that is supposed to have mixed (or non-LF) line endings in the repository. It’s really only useful in combination with core.autocrlf (to make sure that its automatic guesses can’t destroy anything), and if you’re setting your own attributes via .gitattributes it should be okay to turn all that off.