Add CI to test po files

Stuart Prescottrequested to merge
stuart/debian-reference:tmp/add-ci into master

This pipeline runs 'make wrap; make po; make test' as per the instructions in README.md for how to test out the po files. It will fail if the po files are syntactically incorrect or if the toolchain beneath those tests changes in an incompatible way.

The PDFs are not generated in order to keep the duration of the tests down. It takes approximately 7 min to run.

Note that the CI will currently fail until the tools are ported to Python 3.

Merge request reports