DOC: DataFrameGroupBy.idxmin() returns DataFrame, documentation says Serie #20763

Job	Run time
Linux-32-bit	19m 1s
Pyodide build	23m 41s
python-freethreading	22m 39s
Linux-Musl	17m 17s
python-dev (macOS-14)	15m 0s
python-dev (macOS-13)	23m 41s
python-dev (ubuntu-22.04)	22m 16s
python-dev (windows-latest)	23m 40s
macos-13 actions-310.yaml	23m 42s
macos-13 actions-311.yaml	23m 48s
macos-14 actions-310.yaml	21m 13s
macos-14 actions-311.yaml	21m 57s
macos-14 actions-312.yaml	22m 50s
macos-13 actions-312.yaml	23m 24s
windows-latest actions-311.yaml	23m 22s
windows-latest actions-312.yaml	23m 22s
windows-latest actions-310.yaml	23m 22s
ubuntu-latest actions-310.yaml	28m 9s
Minimum Versions	22m 39s
ubuntu-latest actions-311.yaml	28m 10s
Future infer strings (without pyarrow)	23m 25s
Locale: zh_CN	23m 42s
Locale: it_IT	23m 12s
Downstream Compat	5m 51s
Numpy Dev	16m 33s
Pyarrow Nightly	19m 4s
Pypy	1m 11s
ubuntu-latest actions-312.yaml	28m 10s
Future infer strings	23m 26s
	10h 17m 47s

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