Tests: Require imagejpeg() function in WP_Widget_Media_Image::render_media() test.

This outputs a proper message if the requirement is not met, instead of an obscure failure further in the test.

This test relies on multiple resized copies of a test JPEG image being generated and available.

Follow-up to [49010], [49024], [49025], [49045], [49050].

See #50639, #50640.

git-svn-id: https://develop.svn.wordpress.org/trunk@49052 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/widgets/media-image-widget.php

@@ -408,6 +408,7 @@ class Test_WP_Widget_Media_Image extends WP_UnitTestCase {
 	 * Test render_media method.
 	 *
 	 * @covers WP_Widget_Media_Image::render_media
+	 * @requires function imagejpeg
 	 */
 	function test_render_media() {
 		$widget = new WP_Widget_Media_Image();