chore: update Sphinx version to 5.3

[kenjis]

Description

Running Sphinx v4.5.0

Sphinx version error:
The sphinxcontrib.devhelp extension used by this project needs at least Sphinx v5.0; it therefore cannot be built with this version.
make: *** [Makefile:20: html] Error 2
Traceback (most recent call last):
  File "/entrypoint.py", line 22, in <module>
    action.build_all_docs(github_env, [os.environ.get("INPUT_DOCS-FOLDER")])
  File "/sphinx_action/action.py", line 167, in build_all_docs
    raise RuntimeError("Build failed")
RuntimeError: Build failed

https://github.com/codeigniter4/CodeIgniter4/actions/runs/7564707135/job/20599261845

Checklist:

• Securely signed commits
• [] Component(s) with PHPDoc blocks, only if necessary or adds value
• [] Unit testing, with >80% coverage
• [] User guide updated
• [] Conforms to style guide