Update sphinx and associated dependencies.

This ensures that Sphinx runs on the latest Python version packaged with
Ubuntu LTS.

sphinx/tools/requirements.txt

@@ -1,24 +1,26 @@
-alabaster==0.7.12
-Babel==2.9.1
-certifi==2020.12.5
-chardet==4.0.0
-docutils==0.16
-idna==2.10
-imagesize==1.2.0
-Jinja2==3.0.1
-MarkupSafe==2.0.1
-packaging==20.9
-Pygments==2.9.0
-pyparsing==2.4.7
-pytz==2021.1
-requests==2.25.1
-snowballstemmer==2.1.0
-Sphinx==4.0.2
-sphinx-rtd-theme==0.5.2
-sphinxcontrib-applehelp==1.0.2
+alabaster==0.7.13
+Babel==2.12.1
+certifi==2022.12.7
+charset-normalizer==3.1.0
+docutils==0.18.1
+idna==3.4
+imagesize==1.4.1
+Jinja2==3.1.2
+MarkupSafe==2.1.2
+packaging==23.0
+Pygments==2.14.0
+requests==2.28.2
+snowballstemmer==2.2.0
+Sphinx==6.1.3
+sphinx-rtd-theme==1.2.0
+sphinxcontrib-applehelp==1.0.4
 sphinxcontrib-devhelp==1.0.2
-sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-htmlhelp==2.0.1
+sphinxcontrib-jquery==4.1
 sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-qthelp==1.0.3
-sphinxcontrib-serializinghtml==1.1.4
-urllib3==1.26.4
+sphinxcontrib-serializinghtml==1.1.5
+urllib3==1.26.15
+importlib-metadata==6.1.0
+pytz==2023.2
+typing-extensions==4.5.0