DOC: Run doctests for pandas/plotting
- [x] closes #22459



Failure unrelated. Looks mamba related

```

Updating 'pandas-dev' env from conda env update...
  /usr/share/miniconda/condabin/mamba env update --name pandas-dev --file ci/deps/actions-38-db.yaml
  
  
  Looking for: ['python=3.8', "cython[version='>=0.29.24']", "pytest[version='>=6.0']", "pytest-xdist[version='>=1.31']", "hypothesis[version='>=5.5.3']", "pytest-cov[version='>=2.10.1']", "aiobotocore[version='<2.0.0']", 'beautifulsoup4', 'boto3', "botocore[version='>=1.11']", 'dask', "fastparquet[version='>=0.4.0']", "fsspec[version='>=0.7.4']", "gcsfs[version='>=0.6.0']", 'geopandas', 'html5lib', 'matplotlib', 'nomkl', 'numexpr', 'numpy=1.18', 'odfpy', 'openpyxl', 'pandas-gbq', 'psycopg2', "pyarrow[version='>=1.0.1']", 'pymysql', 'pytables', 'pytorch', 'python-snappy', 'python-dateutil', 'pytz', "s3fs[version='>=0.4.0']", 'scikit-learn', 'scipy', 'sqlalchemy', 'statsmodels', 'xarray', 'xlrd', 'xlsxwriter', 'xlwt', 'brotlipy', 'coverage', 'pandas-datareader', 'pyxlsb']
  
  
  Encountered problems while solving:
    - nothing provides openblas 0.3.5.* needed by libblas-3.8.0-4_openblas
  
  pkgs/main/noarch          
  pkgs/r/linux-64           
  pkgs/r/noarch             
  pkgs/main/linux-64        
  conda-forge/noarch        
  conda-forge/linux-64  
```