Rename the unity job to lint and widen what it checks.

Unity is how two of the checks are built rather than what any of them look for, and the job had already grown a check that does not need a unity build at all. lint describes the whole set and pairs with the code-format job below it.

Drop debug from the unused parameter build. Asserts are compiled out of a release build, so a parameter that only an assert reads is reported along with a parameter that nothing reads at all. Both are marked the same way, with a void cast that shows ignoring the parameter is intended.

Add libssh2 so the SFTP driver is built. Without it HAVE_LIBSSH2 is undefined and the driver is preprocessed away, so none of these checks were looking at it.