PHPCS: Implement StaticClosure rule

phpcs.xml.dist

@@ -125,6 +125,7 @@
   <rule
     ref="SlevomatCodingStandard.TypeHints.NullableTypeForNullDefaultValue"
   />
+  <rule ref="SlevomatCodingStandard.Functions.StaticClosure" />
   <!-- Enforce no space between closing brace and colon of return typehint. -->
   <rule ref="SlevomatCodingStandard.TypeHints.ReturnTypeHintSpacing">
     <properties>

tests/phpunit/integration/tests/AMP/Sanitization.php

@@ -505,7 +505,7 @@ public function test_get_sanitizers_with_dev_mode(): void {
 		$validation_error_callback = [ $this->instance, 'validation_error_callback' ];
 		add_filter(
 			'web_stories_amp_dev_mode_element_xpaths',
-			fn( $xpaths ) => array_merge( $xpaths, $element_xpaths )
+			static fn( $xpaths ) => array_merge( $xpaths, $element_xpaths )
 		);
 
 		// Check that AMP_Dev_Mode_Sanitizer is not registered if not in dev mode.

tests/phpunit/integration/tests/Infrastructure/LazilyInstantiatedServiceTest.php

@@ -27,7 +27,7 @@ public function test_it_can_return_the_actual_service_it_represents(): void {
 	}
 
 	public function test_it_throws_when_instantiating_an_invalid_service(): void {
-		$callable     = fn() => new stdClass();
+		$callable     = static fn() => new stdClass();
 		$lazy_service = new LazilyInstantiatedService( $callable );
 
 		$this->expectException( InvalidService::class );