workflows/eval: test all available versions

With this change, we start running Eval on all available Lix and Nix
versions. Because this requires a lot of resources, this complete test
is only run when `ci/pinned.json` is updated.

The resulting outpaths are checked for consistency with the target
branch. A difference will cause the `report` job to fail, thus blocking
the merge, ensuring Eval consistency for Nixpkgs across different
versions.

This implements a kind of "ratchet style" check: Since we originally
confirmed that the versions currently in Nixpkgs at the time of this
commit match Eval behavior of Nix 2.3, we can ensure consistency with
Nix 2.3 down the road, even without testing for it explicitly.

There had been one regression in Eval consistency for Nix between 2.18
and 2.24 - two tests in `tests.devShellTools` produce different results
between Lix 2.91+ (which was forked from Nix 2.18) and Nix 2.24+. I
assume it's unlikely that such a change would be "fixed" by now, thus I
added an exception for these.

As a bonus, we also present the total time in seconds it takes for Eval
to complete for every tested version in a summary table. This allows us
to easily see performance improvements for Eval due to version updates.
At this stage, this time only includes the "outpaths" step of Eval, but
not the generation of attrpaths beforehand.

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