test: Only request client certificate when needed in test-httpstream
test: Only request client certificate when needed in test-httpstream

glib-networking 2.61.1 breaks `G_TLS_AUTHENTICATION_REQUESTED`, see
<https://gitlab.gnome.org/GNOME/glib-networking/issues/92>.

It is basically impossible to check the glib-networking version in an
upstream compatible way. Also, client certificates are off by default,
so it is fair to run tests that don't provide a client certificate
against a web server that doesn't request one.

Closes #12274
mvollmer/cockpit,martinpitt/cockpit,cockpituous/cockpit,mvollmer/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,mvollmer/cockpit,cockpituous/cockpit,garrett/cockpit,martinpitt/cockpit,deryni/cockpit,cockpituous/cockpit,garrett/cockpit,moraleslazaro/cockpit,deryni/cockpit,cockpituous/cockpit,cockpit-project/cockpit,cockpituous/cockpit,garrett/cockpit,deryni/cockpit,mvollmer/cockpit,deryni/cockpit,garrett/cockpit,deryni/cockpit,garrett/cockpit,deryni/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,deryni/cockpit,moraleslazaro/cockpit