CrateDB Guide Configuration: Do not set `language = ""`

[amotl]

Setting language = "" causes downstream havoc.

Exception occurred:
  File "/Users/amo/dev/crate/docs/cratedb-guides/docs/.crate-docs/.venv/lib/python3.12/site-packages/docutils/parsers/rst/directives/parts.py", line 75, in run
    name = language.labels['contents']
           ^^^^^^^^^^^^^^^
AttributeError: module 'docutils.languages' has no attribute 'labels'

https://github.com/crate/crate-docs-theme/blob/f33bb4f7d1249af58331c702538b4baa072da062/src/crate/theme/rtd/conf/cratedb_guide.py#L34-L36

[amotl]

Fixed with GH-491.