client: Set a source tag for all tasks
This makes it a lot simpler to identify what went wrong, e.g. what was before:
GTask 0x55c4c3d64650 (source object: 0x55c4c3d51ab0, source tag: (nil)) finalized without ever returning (using g_task_return_*()). This potentially indicates a bug in the program.
is now:
Task matrix_start_sync (source object: 0x564c003d8ae0, source tag: 0x564bff80cab0) finalized without ever returning (using g_task_return_*()). This potentially indicates a bug in the program. ^^^^^^^^^^^^^^^^^^^^^^