fix: don't close menu on blur when focus moves to an element inside the menu

[shxwat]

Summary

Fixes #5508 — with closeMenuOnSelect={false} (commonly used for a checkbox-style custom multi-select Option), clicking a focusable element inside a custom Option (e.g. a <label>/<input type="checkbox">) moves DOM focus onto that element. This fires onInputBlur on the hidden search input, which unexpectedly closes the menu even though closeMenuOnSelect is false.

Root cause

onInputBlur already had a guard meant to handle exactly this case — refocus the input instead of closing the menu if focus moved to something inside the menu list:

if (this.menuListRef && this.menuListRef.contains(document.activeElement)) {
  this.inputRef!.focus();
  return;
}

The problem is that document.activeElement is not guaranteed to already reflect the newly-focused element at the point the blur handler runs synchronously — this is inconsistent across browsers/timing, which is why the bug is intermittent and hard to pin down (see the multiple "+1, same issue" reports on #5508 over the last few years).

Fix

Also check the blur event's relatedTarget, which the browser sets to the element about to receive focus, and is reliable for this purpose:

if (
  this.menuListRef &&
  (this.menuListRef.contains(document.activeElement) ||
    this.menuListRef.contains(event.relatedTarget as Node))
) {
  this.inputRef!.focus();
  return;
}

Test plan

• Added a regression test (Select.test.tsx) that renders an open menu, fires a blur on the input with relatedTarget set to an option element inside the menu, and asserts onMenuClose is not called. Confirmed this test fails without the fix and passes with it.
• Ran the full Select/Async/AsyncCreatable/Creatable/StateManaged jest suites locally (npx jest packages/react-select/src/__tests__/) — 256 passed, 3 skipped (pre-existing), no regressions.
• Added a changeset.

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🦋 Changeset detected

Latest commit: 6cb978c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
react-select	Patch

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