build: Use coverage only in src/ directory
build: Use coverage only in src/ directory

We are only interested in seeing the coverage of the main code, not the
coverage of tests or other irrelevant code.

MathieuDuponchelle/grilo-plugins,MikePetullo/grilo-plugins,MathieuDuponchelle/grilo-plugins,grilofw/grilo-plugins,vrutkovs/grilo-plugins,grilofw/grilo-plugins,MathieuDuponchelle/grilo-plugins,MikePetullo/grilo-plugins,vrutkovs/grilo-plugins,jasuarez/grilo-plugins,jasuarez/grilo-plugins,MathieuDuponchelle/grilo-plugins,vrutkovs/grilo-plugins,GNOME/grilo-plugins,MikePetullo/grilo-plugins,GNOME/grilo-plugins,vrutkovs/grilo-plugins