Bump Sphinx version to 5.3.0
Make the Sphinx version listed in doc/arm/requirements.txt match the version currently used in GitLab CI, so that Read the Docs builds the documentation using the same Python software versions as those used in GitLab CI.
Make the Sphinx version listed in doc/arm/requirements.txt match the version currently used in GitLab CI, so that Read the Docs builds the documentation using the same Python software versions as those used in GitLab CI.