Switch language from None to "en" in docs build (#721)

Needed for Sphinx 5 compatibility. Should fix the following warning occurring in doc builds.

```
Invalid configuration value found: 'language = None'. Update your configuration to a valid langauge code. Falling back to 'en' (English).
```

xref: sphinx-doc/sphinx#10481

Authors:
  - GALI PREM SAGAR (https://github.com/galipremsagar)

Approvers:
  - Corey J. Nolet (https://github.com/cjnolet)
  - Ray Douglass (https://github.com/raydouglass)

URL: #721

ci/release/update-version.sh

@@ -37,6 +37,10 @@ sed_runner 's/'"pyraft_version .*)"'/'"pyraft_version ${NEXT_FULL_TAG})"'/g' pyt
 sed_runner 's/'"branch-.*\/RAPIDS.cmake"'/'"branch-${NEXT_SHORT_TAG}\/RAPIDS.cmake"'/g' cpp/CMakeLists.txt
 sed_runner 's/'"branch-.*\/RAPIDS.cmake"'/'"branch-${NEXT_SHORT_TAG}\/RAPIDS.cmake"'/g' python/pylibraft/CMakeLists.txt
 
+# Docs update
+sed_runner 's/version = .*/version = '"'${NEXT_SHORT_TAG}'"'/g' docs/source/conf.py
+sed_runner 's/release = .*/release = '"'${NEXT_FULL_TAG}'"'/g' docs/source/conf.py
+
 for FILE in conda/environments/*.yml; do
   sed_runner "s/dask-cuda=${CURRENT_SHORT_TAG}/dask-cuda=${NEXT_SHORT_TAG}/g" ${FILE};
   sed_runner "s/rapids-build-env=${CURRENT_SHORT_TAG}/rapids-build-env=${NEXT_SHORT_TAG}/g" ${FILE};

docs/source/conf.py

@@ -84,16 +84,16 @@
 # built documents.
 #
 # The short X.Y version.
-version = '22.02'
+version = '22.08'
 # The full version, including alpha/beta/rc tags.
-release = '22.02.00'
+release = '22.08.00'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
 #
 # 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.