[Chapel Merge] Update the docs version menu / button to reflect the staged docs for 1.30

Branch: refs/heads/main
Revision: 8941286fffe7d89561f0b8fd75bd31889973c643
Author: bradcray
Link: Update the docs version menu / button to reflect the staged docs for 1.30 by bradcray · Pull Request #21943 · chapel-lang/chapel · GitHub
Log Message:
Update the docs version menu / button to reflect the staged docs for 1.30 (#21943)

[trivial/rote, not reviewed]

This is the normal update when we're staging docs for the pending
release, to make the docs version menu / button reflect those staged
docs.

The diff here is slightly different than the one for
Update docs menu/button to reflect staged release by bradcray · Pull Request #21228 · chapel-lang/chapel · GitHub though it matches the
bestPractices instructions. I'm assuming I did the wrong thing last
time, but if that turns out to be wrong, I'll back that part of the
change out and update the best practices instructions.

Compare: Comparing c69f8015084aa5c9c6af401a86a601c7e741749c...84383e6e6bbb72cb744db7ea4f758c5ed4b98d3b · chapel-lang/chapel · GitHub

Diff:
M doc/rst/conf.py
M doc/util/versionButton.php
https://github.com/chapel-lang/chapel/pull/21943.diff