tests: Add simple test to load stylesheet
Stylesheet changes trigger warnings ever so often, add a test to catch these early. E.g. !1122 (merged) would have shown:
$ meson test -C _build/ --print-errorlogs css
...
1/1 phosh:unit / css FAIL 0.37s killed by signal 5 SIGTRAP
...
stderr:
(/var/scratch/librem5/phosh/_build/tests/test-css:75236): Gtk-WARNING **: 21:22:54.784: Theme parsing error: common.css:513:15: Invalid name of pseudo-class
/cc @snwh since this hopefully make your work simpler
Edited by Guido Günther