Fix build of Read the Docs on latest

[lubojr]

Build does not run with https://readthedocs.org/projects/eoxserver/builds/20102333/

django.core.exceptions.ImproperlyConfigured: SpatiaLite requires SQLite to be configured to allow extension loading.

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/eoxserver/envs/master/lib/python3.10/site-packages/sphinx/cmd/build.py", line 279, in build_main
    app = Sphinx(args.sourcedir, args.confdir, args.outputdir,
  File "/home/docs/checkouts/readthedocs.org/user_builds/eoxserver/envs/master/lib/python3.10/site-packages/sphinx/application.py", line 202, in __init__
    self.config = Config.read(self.confdir, confoverrides or {}, self.tags)
  File "/home/docs/checkouts/readthedocs.org/user_builds/eoxserver/envs/master/lib/python3.10/site-packages/sphinx/config.py", line 173, in read
    namespace = eval_config_file(filename, tags)
  File "/home/docs/checkouts/readthedocs.org/user_builds/eoxserver/envs/master/lib/python3.10/site-packages/sphinx/config.py", line 364, in eval_config_file
    raise ConfigError(msg % traceback.format_exc()) from exc
sphinx.errors.ConfigError: There is a programmable error in your configuration file:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/eoxserver/envs/master/lib/python3.10/site-packages/django/contrib/gis/db/backends/spatialite/base.py", line 42, in get_new_connection
    conn.enable_load_extension(True)
AttributeError: 'sqlite3.Connection' object has no attribute 'enable_load_extension'