Update Sphinx version

[ramonfigueiredo]

• Update Sphinx version to 5.0.0 on docs/requirements.txt
• Change docs/conf.py to use language = 'en'

[ramonfigueiredo]

Update Sphinx version

This update addresses the failure in the "Test Documentation Build" workflow due to outdated Sphinx requirements.

The workflow was not compatible with Sphinx v4.3.1, as the minimum required version is now Sphinx v5.0.0. Additionally, Sphinx v5.0.0 mandates specifying a valid language setting, unlike the previous allowance for a None value.

Modifications made

1. Updated the Sphinx version in docs/requirements.txt by replacing sphinx==4.3.1 with sphinx==5.0.0
2. Altered docs/conf.py to set the documentation language explicitly. Changed language = None to language = 'en' to meet the new requirements of Sphinx v5.0.0