Disable /speculative_auth tests when SASL is disabled

[eramongodb]

My understanding is that the speculative auth tests require SASL for correct behavior, but are not being disabled when SASL is disabled. This PR adds a MONGOC_ENABLE_SASL check in addition the existing MONGOC_ENABLE_CRYPTO check to avoid running SASL tests when crypto is enabled but SASL is disabled (not a normal/expected configuration, but nevertheless).

[kevinAlbs]

I think this check is not necessary.

The C driver SASL library dependency (indicated by MONGOC_ENABLE_SASL) is only required to implement the authMechanism's GSSAPI and PLAIN. Authentication notes:

Note The MongoDB C Driver must be compiled with SASL support in order to use SASL PLAIN authentication.

Note On UNIX-like environments, Kerberos support requires compiling the driver against cyrus-sasl.
On Windows, Kerberos support requires compiling the driver against Windows Native SSPI or cyrus-sasl. The default configuration of the driver will use Windows Native SSPI.

Speculative authentication only applies to the authMechanism's MONGODB-X509, SCRAM-SHA-1 and SCRAM-SHA-256. DRIVERS-918 notes:

Speculative authentication is ignored for server versions less than or equal to 4.2 and is supported for X.509, SCRAM-SHA-1 and SCRAM-SHA-256.

[eramongodb]

Observed issue is better addressed by #1214.