BUG/MINOR: ssl: don't uppercase the native group name

BUG/MINOR: ssl: don't uppercase the native group name

The change to SSL_get0_group_name() assumed that its output differed
from SSL_get_negotiated_group() followed by OBJ_nid2sn() only in
case. This is true for x25519/X25519 and x448/X448, but cannot be
generalized to other groups.

For P-256, the APIs return secp256r1 and prime256v1 respectively:
these are aliases, not a case difference. For P-384 and P-521, both
APIs already return secp384r1 and secp521r1, so uppercasing actually
introduces a mismatch. It also changes native mixed-case hybrid names
such as SecP256r1MLKEM768.

Moreover, SSL_get0_group_name() returns a library-owned string shared
through the SSL_CTX. Uppercasing it in place modifies OpenSSL state
and risks concurrent access to that string.

Remove the uppercase conversion and return the native name unchanged.

This should not be backported as it would could break matching of the
curves.