Update requirements to add PyStemmer to doc-requirements and environment (matplotlib#29019)

* Update requirements to add PyStemmer to doc-requirements and environment

* Update requirements to add PyStemmer to doc-requirements and environment

---------

Co-authored-by: Ancheng <[email protected]>

Author: Anson0028

environment.yml

@@ -43,6 +43,7 @@ dependencies:
   - joblib  # needed for sphinx-gallery[parallel]
   - sphinx-design
   - sphinx-tags>=0.4.0
+  - pystemmer
   - pip
   - pip:
       - mpl-sphinx-theme~=3.8.0

requirements/doc/doc-requirements.txt

@@ -17,6 +17,7 @@ packaging>=20
 pydata-sphinx-theme~=0.15.0
 mpl-sphinx-theme~=3.9.0
 pyyaml
+PyStemmer
 sphinxcontrib-svg2pdfconverter>=1.1.0
 sphinxcontrib-video>=0.2.1
 sphinx-copybutton