TST: sql add tests for NaN handling
DOC: tiny groupby.rst edit
TYPO: idxmax is maximum, not minimum

Confusing doc typo was momentarily confusing.
Merge pull request #7102 from gruen/master

TYPO: idxmax is maximum, not minimum
TST: fixup windows test from GH7092
Merge pull request #7100 from jorisvandenbossche/sql-tests

TST: sql add more tests (NaN handling, ..)
BUG: GroupBy doesnt preserve timezone