CI: test coverage takes up too much space

[stertooy]

A single run of the test suite with coverage enabled, results in a 17 GB coverage folder. As GitHub runners have limited disk space available, and we run through the tests twice, this causes the tests to fail.

[fingolfin]

Wow that's a lot. My guess is that because the "data" files in data are GAP code, we produce coverage data for them, and there are > 200 MB in there... Perhaps we could compress the coverage files we generate... or turn it off for that dir... or turn it off completely.

Or do you approach in #36, also file