Improve _add_member() #6003

Job	Run time
Cache identify	6s
Shellcheck	6s
Dependency	5s
Prepare	7s
Ruff check and force	7s
Check commit	19s
Run pytest using Python ${{ matrix.python-version }}	-1s
Run mypy	-1s
Process test coverage	0s
Build and publish Python 🐍 distributions 📦 to TestPyPI	0s
Process test complexity	0s
	48s

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