DOC: add select_dtypes case to 3.0 string migration guide#62403

mroeschke merged 1 commit intopandas-dev:mainpandas-dev/pandas:mainfrom

jorisvandenbossche:string-dtype-select-dtypes-migration-guidejorisvandenbossche/pandas:string-dtype-select-dtypes-migration-guideCopy head branch name to clipboard