Tests: Replace the timezone used in date/time tests.

The `Europe/Kiev` timezone has been deprecated in PHP 8.2 and replaced with `Europe/Kyiv`.

The tests updated in this commit are testing the WordPress date/time functionality. They are **not** testing whether WP or PHP can handle deprecated timezone names correctly.

To ensure the tests follow the original purpose, the use of `Europe/Kiev` within these tests is now replaced with the `Europe/Helsinki` timezone, which is within the same timezone as `Europe/Kyiv`. This should ensure that these tests run without issue and test what they are supposed to be testing on every supported PHP version (unless at some point in the future `Europe/Helsinki` would be renamed, but that's a bridge to cross if and when).

Note: Separate tests should/will be added to ensure that relevant date/time related functions handle a deprecated timezone correctly, but that is not something ''these'' tests are supposed to be testing.

Follow-up to [45853], [45856], [45876], [45882], [45887], [45908], [45914], [46577], [46154], [46580], [46864], [46974], [54207].

Props jrf, costdev, SergeyBiryukov.
Merges [54217] to the 6.0 branch.
See #56468.

Built from https://develop.svn.wordpress.org/branches/6.0@54512


git-svn-id: http://core.svn.wordpress.org/branches/6.0@54071 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.0.3-alpha-54430';
+$wp_version = '6.0.3-alpha-54512';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.