tests: fix a mutex-handling bug exposed by new glib

The new futex-based GMutex notices that we were destroying a locked
mutex and complains. Fix that.
tests: update to handle G_PARAM_DEPRECATED warnings in new glib

SoupSession:ssl-ca-file is deprecated, but we were still using it some
tests for convenience, and in others because we need to test that it
still works right. Fix the former by using SoupSession:tls-database
instead, and fix the later by adjusting the property's GParamSpec's
flags around tests that need to test :ssl-ca-file.
2.47.4