Add seemingly missing image/webp support checks for PHP 7.2

tests/plugins/webp-uploads/helper-tests.php

@@ -215,6 +215,10 @@ public function it_should_prevent_to_create_an_image_size_when_attached_file_doe
 	 * @test
 	 */
 	public function it_should_prevent_to_create_a_subsize_if_the_image_editor_does_not_exists(): void {
+		if ( ! wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
+			$this->markTestSkipped( 'Mime type image/webp is not supported.' );
+		}
+
 		$attachment_id = self::factory()->attachment->create_upload_object(
 			TESTS_PLUGIN_DIR . '/tests/testdata/modules/images/leaves.jpg'
 		);
@@ -269,6 +273,10 @@ static function () {
 	 * @test
 	 */
 	public function it_should_create_an_image_with_filter_webp_uploads_pre_generate_additional_image_source(): void {
+		if ( ! wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
+			$this->markTestSkipped( 'Mime type image/webp is not supported.' );
+		}
+
 		remove_all_filters( 'webp_uploads_pre_generate_additional_image_source' );
 
 		$attachment_id = self::factory()->attachment->create_upload_object( TESTS_PLUGIN_DIR . '/tests/testdata/modules/images/car.jpeg' );