#11645 all rtd formats

[glyph]

Scope and purpose

Fixes #11645

Contributor Checklist:

This process applies to all pull requests - no matter how small.
Have a look at our developer documentation before submitting your Pull Request.

Below is a non-exaustive list (as a reminder):

• The title of the PR should describe the changes and starts with the associated issue number, like “#9782 Remove twisted.news. #1234 Brief description”.
• A release notes news fragment file was create in src/twisted/newsfragments/ (see: Release notes fragments docs.)
• The automated tests were updated.
• Once all checks are green, request a review by leaving a comment that contains exactly the string needs-review.
  Our bot will trigger the review process, by applying the pending review label
  and requesting a review from the Twisted dev team.

[adiroiban]

Maybe add a comment that we have "all" as it should include htmlzip and we want htmlzip for offline docs readers.

Just a help with someone touching this in the future.
Most probably that person will not check the whole history of this line..
and might think that "all" is excessive and html and PDF should be enough.

[glyph]

needs-review

[adiroiban]

Thanks.

Looks good.
I hope RTD build will pass.