Fix upgrade-check false positive for hx-history-elt

[marciomazza]

The upgrade-check tool is incorrectly flagging hx-history-elt as a removed attribute, when it was actually restored in v4 core.

Problem

The REMOVED_ATTRS dictionary in src/scripts/upgrade-check.py contained:

"hx-history-elt": "removed",

This caused the upgrade-check tool to warn users that hx-history-elt should be removed from their HTML, even though it's a valid, working attribute in htmx v4.

Evidence

hx-history-elt was restored to v4 core in commit 2b39a899 (PR #3773):

• "Add back hx-history-elt and improve history cache extension"

The attribute is actively used in src/htmx.js:1636:

let historyElt = document.querySelector(this.__prefixSelector('[hx-history-elt]')) || document.body;

And documented in CHANGELOG.md:

Restored hx-history-elt from htmx 2 and improved the hx-history-cache extension.

Fix

Removed hx-history-elt from the REMOVED_ATTRS dictionary in src/scripts/upgrade-check.py.

Note: dist/scripts/upgrade-check.py is a build copy and isn't updated here, per guidelines; should be regenerated on release.

Testing

The upgrade-check tool will no longer flag hx-history-elt as removed, allowing users to keep this valid attribute in their HTML.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded

[1cg]

Thank you!