fix: Disallow Jinja2 v3.1.0 to avoid nbsphinx triggering attribute er…

…ror (#1824)

* Disallow Jinja2 v3.1.0 to avoid nbsphinx triggering attribute error:
    
    AttributeError: module 'jinja2.utils' has no attribute 'escape'

This is a stopgap measure and this line should be removed as soon as there
is a resolution and new nbsphinx release.
   - c.f. spatialaudio/nbsphinx#641

setup.py

@@ -55,6 +55,7 @@
             'sphinx-click',
             'sphinx_rtd_theme',
             'nbsphinx!=0.8.8',  # c.f. https://github.com/spatialaudio/nbsphinx/issues/620
+            'Jinja2!=3.1.0',  # c.f. https://github.com/spatialaudio/nbsphinx/issues/641
             'ipywidgets',
             'sphinx-issues',
             'sphinx-copybutton>=0.3.2',