Ensure that `Tests_Theme_wpThemeJson::test_set_spacing_sizes_should_detect_invalid_spacing_scale` is compatible with PHPUnit 10

[antonvlasenko]

The test_set_spacing_sizes_should_detect_invalid_spacing_scale() test method is incompatible with PHPUnit 10 because the TestCase::expectNotice() method is deprecated.
The changes from ​https://github.com/WordPress/gutenberg/pull/55354 need to be backported for that test method to Core to ensure compatibility with PHP 10.

[antonvlasenko]

I'm working on a PR for this ticket.

This PR aims to backport ​https://github.com/WordPress/gutenberg/pull/55354 to Core to ensure that Tests_Theme_wpThemeJson::test_set_spacing_sizes_should_detect_invalid_spacing_scale is compatible with PHPUnit 10

Trac ticket: https://core.trac.wordpress.org/ticket/60305#comment:1

[youknowriad]

In 57332:

Editor: Ensure PHPUnit10 compatibility for ThemeJson unit test.

Expecting E_STRICT, E_NOTICE, and E_USER_NOTICE errors is deprecated in PHPUnit 10.
This updates the test to rely on an exception instead.

Props antonvlasenko.
Fixes #60305.

Committed in https://core.trac.wordpress.org/changeset/57332

[kebbet]

Please milestone the ticket to 6.5 @youknowriad, thanks!

[youknowriad]

Good call thanks @kebbet

[desrosj]

Related: #59486.

set_error_handler is a global change that should be cleaned up

Trac ticket: https://core.trac.wordpress.org/ticket/60305

[jorbin]

In 57361:

Build/Tests: Ensure set_error_handler is cleaned up.

Follow up to: [57332].

Fixes #60305.

[antonvlasenko]

@jorbin I believe it might be worth considering a revert of https://core.trac.wordpress.org/changeset/57361, as it appears that its code does not get executed.
The handler is already being cleaned up within the new error handler itself:

		set_error_handler(
			static function ( $errno, $errstr ) {
				restore_error_handler(); // <-- This is where it's cleared up.
				throw new Exception( $errstr, $errno );
			},
			E_ALL
		);