more fixes

Author: cvanelteren

ultraplot/tests/test_thread_safety.py

@@ -9,6 +9,7 @@ def modify_rc_on_thread(prop: str, value=None, with_context=True):
         with uplt.rc.context(**{prop: value}):
             assert uplt.rc[prop] == value, f"Thread {id} failed to set rc params"
     else:
+        uplt.rc[prop] = value
         assert uplt.rc[prop] == value, f"Thread {id} failed to set rc params"