TLS 1.3 client sigalgs test no longer needs TLS 1.2

Per the TODO comment, we now have proper certificate selection for
TLS 1.3 client certificates, so this test can move into its own
block.  (It cannot merge with the previous block, as it requires EC.)

Verified that the test passes when configured with enable-tls1_3
no-tls1 no-tls1_1 no-tls1_2.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3131)