Enable more checks during CI step
Right now, only "make" is run during the CI pass. This could be made more strict by additionally calling "make check" - which also runs xmllint on the generated (translated) XML.
While discussing this at GUADEC, a group of us also realised that when itstool is run during the "make" pass and comes across a broken translation, where a translator has made a mistake with a translation that contains some XML, a warning is emitted, such as:
Warning: Could not merge de translation for msgid: For a Wi-Fi connection, the <_:media-1/> button will be located next to the active network
These warnings can be made fatal with the "--strict" argument to itstool, but there is currently no easy way to add that (although it might be possible to inject this with the ITSTOOL environment variable). yelp.m4 (or the meson equivalent) would probably have to be modified to make this easier.