CI/DOC: temporary pin environment to python 3.8 (#41092)
CI/DOC: temporary pin environment to python 3.8 (#41092)


pandas-dev/pandas,pandas-dev/pandas,rs2/pandas,jorisvandenbossche/pandas,rs2/pandas,dsm054/pandas,dsm054/pandas,jorisvandenbossche/pandas,dsm054/pandas,gfyoung/pandas,pandas-dev/pandas,dsm054/pandas,datapythonista/pandas,gfyoung/pandas,datapythonista/pandas,jorisvandenbossche/pandas,rs2/pandas,dsm054/pandas,jorisvandenbossche/pandas,gfyoung/pandas,gfyoung/pandas,rs2/pandas,pandas-dev/pandas,gfyoung/pandas,datapythonista/pandas,datapythonista/pandas