ENH: pre-commit: Prevent add .txx files.
ENH: pre-commit: Prevent add .txx files.

A transition occurred in the toolkit to move all .txx files to .hxx files.
This prevents accidental additions of or renames to .txx files.

Change-Id: Id4ace9cfca2c56506d93396366d146173e015003

Sprunth/RGG,Sprunth/RGG,Sprunth/RGG,Sprunth/RGG