Docs: Fix the Lua page header

[kurtmckee]

Pull Request check-list

• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?

Description of change

The Lua scripting page header had too few underlines to qualify as a header and rendered poorly. It also caused each of the individual subheaders to appear in the sidebar as separate pages.

Before

Header:

Sidebar:

After

Header:

Sidebar:

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.40%. Comparing base (6ece1c9) to head (5ddacd4).
⚠️ Report is 37 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #287      +/-   ##
==========================================
- Coverage   76.40%   76.40%   -0.01%     
==========================================
  Files         129      129              
  Lines       34065    34065              
==========================================
- Hits        26029    26027       -2     
- Misses       8036     8038       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.