package/python3: uClibc-ng doesn't set errno when encryption method is not available

Since commit [1] in cpython, an exception is raised when an encryption method
is not available. This eception is handled only if errno is set to EINVAL by
crypt() but uClibc-ng doesn't set errno in crypt() [2].

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/830981961
https://gitlab.com/buildroot.org/buildroot/-/jobs/830981979

[1] https://github.com/python/cpython/commit/0d3fe8ae4961bf551e7d5e42559e2ede1a08fd7c
[2] https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/libcrypt/crypt.c?h=v1.0.36#n29



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>