Update CI with testing framework from eigen_ci_cross_testing.

Antonio Sánchezrequested to merge
cantonios/eigen:ci into master

Merging in test CI from https://gitlab.com/libeigen/eigen_ci_cross_testing.

Now that all tests are green, we should move it to this main repo.

Tested on the main Eigen repo here: https://gitlab.com/libeigen/eigen/-/pipelines/1106209054

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