gmpy2 sees test failures with mpfr 4.2.1, independent of the architecture, see for example

https://ci.debian.net/data/autopkgtest/testing/amd64/p/python-gmpy2/37232406/log.gz

mostly it's a missing "-", however there are a few tests in test_mpc.txt, which look suspicious with the double plus sign ...

Differences (ndiff with -expected +actual):
- mpc('inf+infj')
+ mpc('inf++infj')
? +