Development: Fix documentation build warnings

[b-fein]

Checklist

General

• Language: I followed the guidelines for inclusive, diversity-sensitive, and appreciative language.
• I chose a title conforming to the naming conventions for pull requests.

Motivation and Context

The documentation build produced some warnings.

Description

Fixes those warnings:

• pyris: yml → yaml to fix code block syntax highlighting
• cypress: remove trailing spaces to fix ‘unexpected indentation’ warning
• setup: fix header underline length
• mobile-applications: use an anonymous link (two underscores at the end) instead of a named one to resolve warning about duplicate link targets

Steps for Testing

Build the documentation locally with

cd docs
make clean
make html

Review Progress

Code Review

• Code Review 1
• Code Review 2

[Strohgelaender]

Can we add a GitHub action that fails if such warnings exist? While I appreciate the effort, you should not need to constantly open PRs like this.

[Strohgelaender]

lgtm