doc: switch to the alabaster theme

Beauty is in the eye of the beholder, but the alabaster theme just looks
nicer and leaner.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>

.gitlab-ci.yml

@@ -26,7 +26,7 @@ container-build:
     - .maintainer-tools.fedora:40
   stage: containers
   variables:
-    FDO_DISTRIBUTION_PACKAGES: 'ShellCheck python3-docutils python3-sphinx make python3-sphinx_rtd_theme graphviz'
+    FDO_DISTRIBUTION_PACKAGES: 'ShellCheck python3-docutils python3-sphinx make graphviz'
 
 ###### build
 

conf.py

@@ -25,4 +25,4 @@ root_doc = 'index'
 # -- Options for HTML output -------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-html-output
 
-html_theme = 'sphinx_rtd_theme'
+html_theme = 'alabaster'