Warn about refs in add_event_handler #835

Job	Run time
Test Linting	14s
Test Codegen	48s
Test Imports	16s
Test Docs	33s
Test Examples	1m 18s
Test PyInstaller	1m 45s
Build sdist	34s
Build wheels on ubuntu-latest	1m 35s
Build wheels on windows-latest	4m 5s
Build wheels on macos-latest	2m 30s
Test Linux py37	1m 5s
Test Linux py38	1m 6s
Test Linux py39	1m 7s
Test Linux py310	1m 5s
Test Linux py311	2m 40s
Publish to Github and Pypi	0s
	20m 41s

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