Update documentation dependencies (#3118)

Furo, myst-parser, and Sphinx (had to pin docutils due to sphinx breakage)

docs/conf.py

@@ -87,7 +87,7 @@ def make_pypi_svg(version: str) -> None:
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = None
+language = "en"
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.

docs/requirements.txt

@@ -1,7 +1,9 @@
 # Used by ReadTheDocs; pinned requirements for stability.
 
-myst-parser==0.17.2
-Sphinx==4.5.0
+myst-parser==0.18.0
+Sphinx==5.0.1
+# Older versions break Sphinx even though they're declared to be supported.
+docutils==0.18.1
 sphinxcontrib-programoutput==0.17
 sphinx_copybutton==0.5.0
-furo==2022.4.7
+furo==2022.6.4.1