Run passthru.tests on hydra, so we can spot failures there and make the fetchgit tests a channel blocker.

This adds approximately 400 derivations for x86_64-linux and presumably slightly smaller amounts for other systems. The tests are usually sanity checks written by us, so they are generally quick. Their outputs are virtually empty.

This could work like packageTests in #136022 but with special handling of

• license, to avoid uploading illegal deps
• hydraPlatforms, to avoid attempts to build on unsupported systems
• more?

Possible solutions:
a. copy the relevant meta stuff while constructing pkgs.packageTests. Add recurseIntoAttrs.
b. use the same traversal but apply it to all of release.nix instead of using recurseIntoAttrs.

The latter seems more elegant, as it reuses existing hydra-adjacent logic.

Notify maintainers

@edolstra @grahamc

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute: packageTests
# a list of nixos modules affected by the problem
module: