Backport !4038 "gdbusconnection: Don't deliver signals if the sender doesn't match" to glib-2-72

As other backports of !4038 (merged), for downstreams to consume it and to be linked to the fixed bug.

However, closing it since we won't update the gnome-2-72 branch as per !4041 (comment 2105609)

Fixes: #3268 (closed)