[master] Fixed first link of the navigation bar "On this page" when using docutils>=0.17

[vamera]

Description

This PR fixes on the release branch master the problem reported on #6453.

Checks

Docs building

• Compiles without warnings.

Code formatting and web optimization

• Uses three spaces indentation.
• Adds or updates meta descriptions accordingly.
• Updates the redirects.js script if necessary (check this guide).

Writing style

• Uses present tense, active voice, and semi-formal registry.
• Uses short, simple sentences.
• Uses bold for user interface elements, italics for key terms or emphasis, and code font for Bash commands, file names, REST paths, and code.

[javimed]

#6479 should be solved first

[s-ocando]