Speed up gitlab's CI

Currently, the CI is taking 3 minutes: 1 minute for the linting part, and two minutes for the testsuite (a bit more than 1 minute for Debian and 2 minutes and a half for Fedora one).

It would be nice to reduce a bit the duration of the Fedora part, and to lower the CI duration to about two minutes. One minute would be amazing ♥

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