BUG: groupby.groups with NA categories fails #23099

Job	Run time
Pyodide build	23m 40s
Linux-Musl	16m 19s
Linux-32-bit	18m 22s
python-freethreading	21m 57s
python-dev (macOS-13)	32m 54s
python-dev (macOS-14)	10m 32s
python-dev (ubuntu-22.04)	19m 55s
python-dev (windows-latest)	22m 18s
macos-13 actions-310.yaml	32m 28s
macos-13 actions-311.yaml	27m 11s
macos-13 actions-312.yaml	28m 0s
macos-14 actions-310.yaml	15m 28s
macos-14 actions-311.yaml	15m 29s
macos-14 actions-312.yaml	14m 49s
windows-latest actions-312.yaml	1h 12m 8s
windows-latest actions-310.yaml	1h 5m 1s
windows-latest actions-311.yaml	1h 5m 10s
Minimum Versions	23m 36s
Future infer strings (without pyarrow)	38m 18s
Locale: zh_CN	23m 26s
Locale: it_IT	23m 46s
Downstream Compat	5m 44s
Numpy Dev	16m 46s
Pyarrow Nightly	20m 19s
Pypy	1m 23s
Future infer strings	45m 10s
ubuntu-22.04 actions-310.yaml	45m 49s
ubuntu-22.04 actions-311.yaml	42m 13s
ubuntu-22.04 actions-312.yaml	44m 41s
ubuntu-24.04-arm actions-311.yaml	34m 4s
ubuntu-24.04-arm actions-312.yaml	34m 46s
ubuntu-24.04-arm actions-310.yaml	35m 33s
	15h 37m 15s

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