Do not leave stale OpenSSL errors in _hashlib #159815

Bug report

raise_unsupported_algorithm_impl() peeks the OpenSSL error queue but does not clear it on the ERR_R_UNSUPPORTED and ERR_R_FETCH_FAILED branches. Only the default: branch clears it, via raise_ssl_error_f(). The leftover entry is then reported by the next unrelated failure in the same thread:

>>> import _hashlib
>>> _hashlib.scrypt(b"", salt=b"", n=1024, r=0, p=1)
ValueError: invalid parameter combination for n, r, p, and maxmem
>>> _hashlib.new("no_such_algorithm_xyz")
UnsupportedDigestmodError: [digital envelope routines] unsupported hash algorithm no_such_algorithm_xyz
>>> _hashlib.scrypt(b"", salt=b"", n=1024, r=0, p=1)
ValueError: [digital envelope routines] unsupported

get_asn1_utf8name_by_nid() has the same problem. It decides whether to fall back to the short name based on ERR_peek_last_error(), so a leftover error could make it raise instead of falling back.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-159815: do not leave stale OpenSSL errors in _hashlib #159816