Tests: Remove use of E_STRICT.

The `E_STRICT` constant is deprecated as of PHP 8.4 and will be removed in PHP 9.0.

The error level hasn't been in use since PHP 8.0 anyway, so removing the exclusion from the `error_reporting()` setting in the `install.php` script used in the tests should make no difference in practice.

Ref:
* https://wiki.php.net/rfc/deprecations_php_8_4#remove_e_strict_error_level_and_deprecate_e_strict_constant

Follow-up to [25002].

Props jrf.
See #62061.

git-svn-id: https://develop.svn.wordpress.org/trunk@59068 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/includes/install.php

@@ -4,7 +4,7 @@
  *
  * @todo Reuse the init/load code in init.php
  */
-error_reporting( E_ALL & ~E_DEPRECATED & ~E_STRICT );
+error_reporting( E_ALL & ~E_DEPRECATED );
 
 $config_file_path = $argv[1];
 $multisite        = in_array( 'run_ms_tests', $argv, true );