Sphinx warnings while building

[Piralein]

1. organization\pull_requests\review_guidelines.rst:4: WARNING: duplicate label doc_pr_review_guidelines
   Should be renamed to merge_guidelines

- .. _doc_pr_review_guidelines:
+ .. _doc_pr_merge_guidelines:

2. WARNING: unsupported theme option 'display_version' given

This option is deprecated, I assume it can be removed without problems. We already include the version and language selector as false.
sphinx-rtd-theme.readthedocs.io/en/stable/configuring.html#confval-display_version

3. documentation\guidelines\docs_writing_guidelines.rst:413: WARNING: Lexing literal_block '@onready...#Do stuff' as "gdscript" resulted in an error

We currently don't include the gdscript lexer in this repository, should we add it or remove the .. code-block:: gdscript? (other examples of gdscript are plain text)