Azure CI builds of main failing on rstcheck

[stuartarchibald]

As of 598aadf, main is failing to build in Azure CI in Linux build job configuration py38_np120_doc. The Test step fails with:

# Ensure the README is correctly formatted
if [ "$BUILD_DOC" == "yes" ]; then rstcheck README.rst; fi
Traceback (most recent call last):
  File "/home/vsts/miniconda3/envs/azure_ci/bin/rstcheck", line 5, in <module>
    from rstcheck._cli import main
  File "/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/rstcheck/_cli.py", line 7, in <module>
    from rstcheck_core import _extras, config as config_mod, runner
  File "/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/rstcheck_core/runner.py", line 10, in <module>
    from . import _sphinx, checker, config, types
  File "/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/rstcheck_core/_sphinx.py", line 14, in <module>
    import sphinx.application
  File "/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/sphinx/application.py", line 42, in <module>
    from sphinx.highlighting import lexer_classes, lexers
  File "/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/sphinx/highlighting.py", line 30, in <module>
    from sphinx.ext import doctest
  File "/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/sphinx/ext/doctest.py", line 28, in <module>
    from sphinx.builders import Builder
  File "/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/sphinx/builders/__init__.py", line 24, in <module>
    from sphinx.io import read_doc
  File "/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/sphinx/io.py", line 42, in <module>
    from sphinx.util.rst import append_epilog, docinfo_re, prepend_prolog
  File "/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/sphinx/util/rst.py", line 22, in <module>
    from jinja2 import environmentfilter
ImportError: cannot import name 'environmentfilter' from 'jinja2' (/home/vsts/miniconda3/envs/azure_ci/lib/python3.8/site-packages/jinja2/__init__.py)

looking at the version differences between last working build of main and a failing build, e.g. those in #8544, suggests that jinja2 moving from 3.0 to 3.3 is potentially the cause. This may well be because rstcheck imports sphinx which is pinned to a somewhat old version (2.4.4):

numba/buildscripts/incremental/setup_conda_environment.sh

Line 71 in 598aadf

if [ "$BUILD_DOC" == "yes" ]; then $CONDA_INSTALL sphinx=2.4.4 docutils=0.17 sphinx_rtd_theme pygments numpydoc; fi

and it relies on environmentfilter from jinja2 which is apparently now missing.