Heartbeat: Fix post lock detection race when wp_check_post_lock_window falls below the background heartbeat interval

[Sukhendu2002]

Trac ticket: https://core.trac.wordpress.org/ticket/65171

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[adamsilverstein]

Looks good! Adding some tests would be good.

[adamsilverstein]

Thanks for working on this @Sukhendu2002 — nice fix.

To help land this, I drafted PHPUnit coverage for the new post_lock_window setting in wp_heartbeat_set_suspension() on top of your branch (rebased on current trunk so the test file added in r60520 / 7938204 is present):

https://github.com/adamsilverstein/wordpress-develop/tree/trac-65171-tests

The single test commit is:
adamsilverstein@2139778d90

It adds three cases to Tests_Admin_Includes_Misc_WpHeartbeatSetSuspension_Test:

• post_lock_window is exposed as 150 on post.php and post-new.php.
• post_lock_window is omitted on non-post screens (index.php, edit.php).
• post_lock_window honors the wp_check_post_lock_window filter (verified with a custom value of 60).

Locally: OK (9 tests, 11 assertions).

Feel free to fold these into this PR if you'd like — happy to push to your branch directly if that's easier. Let me know.

[Sukhendu2002]

Thanks @adamsilverstein! I've cherry-picked your test commit into my branch. All tests passing. Appreciate the coverage!