Remove outdated (pre-PEP 517/518) practices in `make check`, fix ci-sage

[mkoeppe]

[dimpase]

seems to be the same story:

2023-10-08T02:43:17.5450390Z   [cysignals-git]     ERROR: Could not find a version that satisfies the requirement setuptools (from versions: none)
2023-10-08T02:43:17.5450681Z   [cysignals-git]     ERROR: No matching distribution found for setuptools
2023-10-08T02:43:17.5451248Z   [cysignals-git]     WARNING: There was an error checking the latest version of pip.
2023-10-08T02:43:17.5451499Z   [cysignals-git]     error: subprocess-exited-with-error