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.

git-svn-id: https://develop.svn.wordpress.org/trunk@57332 602fd350-edb4-49c9-b593-d223f7449a82

Author: youknowriad

tests/phpunit/tests/theme/wpThemeJson.php

@@ -4281,8 +4281,8 @@ public function data_generate_spacing_scale_fixtures() {
 	 * @param array $expected_output Expected output from data provider.
 	 */
 	public function test_set_spacing_sizes_should_detect_invalid_spacing_scale( $spacing_scale, $expected_output ) {
-		$this->expectNotice();
-		$this->expectNoticeMessage( 'Some of the theme.json settings.spacing.spacingScale values are invalid' );
+		$this->expectException( Exception::class );
+		$this->expectExceptionMessage( 'Some of the theme.json settings.spacing.spacingScale values are invalid' );
 
 		$theme_json = new WP_Theme_JSON(
 			array(
@@ -4295,6 +4295,15 @@ public function test_set_spacing_sizes_should_detect_invalid_spacing_scale( $spa
 			)
 		);
 
+		// Ensure PHPUnit 10 compatibility.
+		set_error_handler(
+			static function ( $errno, $errstr ) {
+				restore_error_handler();
+				throw new Exception( $errstr, $errno );
+			},
+			E_ALL
+		);
+
 		$theme_json->set_spacing_sizes();
 		$this->assertSame( $expected_output, _wp_array_get( $theme_json->get_raw_data(), array( 'settings', 'spacing', 'spacingSizes', 'default' ) ) );
 	}