gitlab CI: run the xkeyboard-config rules test tool against evdev.extras.xml

libxkbcommon's parser has an optimization where it stops parsing a file when the required keymap is found. The result of that was that the syntax error fixed in !83 (merged) didn't get detected - all tested layouts where before that erroneous line.

There's only one xkb_symbols map thats below that line but that one is referenced in evdev.extras.xml, not evdev.xml. So let's update our CI to test for that too.