Backport 3.6: Fix some test case dependencies (PEM_C)

[gilles-peskine-arm]

Fix some test case dependencies:

• pk_parse_keyfile_rsa not getting executed
• redundancy on mbedtls_x509_crl_info

PR checklist

Please tick as appropriate and edit the reasons (e.g.: "backport: not needed because this is a new feature")

• [x] changelog no (tests only)
• [x] development https://github.com/Mbed-TLS/mbedtls/pull/9049
• [x] 2.28 backport https://github.com/Mbed-TLS/mbedtls/pull/8929 (came first)
• [x] tests provided

[gilles-peskine-arm]

the PEM version of the new keys (768-784 bits) look like PKCS8 to me. (The pre-existing ones, 1024-4096, look like plain PKCS1 though.)

sigh Thanks for noticing. openssl genrsa changed in OpenSSL 3.0, like openssl rsa. I've fixed the files I generated with OpenSSL 3.0 to be what they say on the tin. Having portable instructions in the makefile is out of scope here, so I just added a note in a comment.