doc: fix build with sphinx 5.0 and later.
Sphinx 5.0 and later fails to build when language is set to None:
Warning, treated as error:
Invalid configuration value found: 'language = None'. Update your configuration to a valid langauge code. Falling back to 'en' (English)
Let's set the language to English since it is the language used for the
documentation.
Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/conf.py b/doc/conf.py
index eac3acc..62c8d31 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -178,7 +178,7 @@
#
# 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'
# There are two options for replacing |today|: either, you set today to some
# non-false value, then it is used: