s2n_tls13_cert_verify_test doesn't run all cases

[jmayclin]

Problem:

A test case is gated behind a compile definition

s2n-tls/tests/unit/s2n_tls13_cert_verify_test.c

Lines 38 to 40 in 89dba0e

	#if RSA_PSS_CERTS_SUPPORTED
	{ .cert_file = S2N_RSA_PSS_2048_SHA256_LEAF_CERT, .key_file = S2N_RSA_PSS_2048_SHA256_LEAF_KEY, .sig_scheme = &s2n_rsa_pss_pss_sha256 },
	#endif

However, the header that defines RSA_PSS_CERTS_SUPPORTED is never included, so it unconditionally evaluates to false, and the RSA-PSS test cases are never executed. Additionally, these test cases fail when the compile definition is corrected.

Previous discussion on this can be seen on the earlier comments in #4430

[maddeleine]

May be an opportunity for try-compile here: #3327.