tests/test-char.c: Wait for the chardev to connect in char_socket_client_dupid_test

tests/test-char.c: Wait for the chardev to connect in char_socket_client_dupid_test

A connecting chardev object has an additional reference by the connecting
thread, so if the chardev is still connecting by the end of the test,
then the chardev object won't be freed. This in turn means that the yank
instance won't be unregistered and when running the next test-case
yank_register_instance will abort, because the yank instance is
already/still registered.

Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <1445e97a5800e3f2ba024ad52b500a0315701632.1609167865.git.lukasstraub2@web.de>
Signed-off-by: Markus Armbruster <armbru@redhat.com>