Unit tests are broken on WordPress trunk due to loading=lazy

[westonruter]

Bug Description

These tests are currently failing in WordPress trunk due to the introduction of loading=lazy (see r47554):

1) AMP_Gallery_Embed_Handler_Test::test__conversion with data set "shortcode_with_lightbox" ('[gallery amp-lightbox=true am...id3}}]', '<style type='text/css'> #gall...</div>')
2) AMP_Gallery_Embed_Handler_Test::test__conversion with data set "shortcode_with_lightbox_linking_to_file" ('[gallery amp-lightbox=true am...id3}}]', '<style type='text/css'> #gall...</div>')
3) Test_AMP_YouTube_Embed_Handler::test__conversion with data set "url_simple" ('https://www.youtube.com/watch...bJY0\n', '<p><amp-youtube data-videoid=...</p>\n', '<p><amp-youtube data-videoid=...</p>\n')
4) Test_AMP_YouTube_Embed_Handler::test__conversion with data set "url_short" ('https://youtu.be/kfVsfOSbJY0\n', '<p><amp-youtube data-videoid=...</p>\n', '<p><amp-youtube data-videoid=...</p>\n')
5) Test_AMP_YouTube_Embed_Handler::test__conversion with data set "url_with_querystring" ('http://www.youtube.com/watch?...=349\n', '<p><amp-youtube data-videoid=...</p>\n', '<p><amp-youtube data-videoid=...</p>\n')
6) Test_AMP_YouTube_Embed_Handler::test__conversion with data set "embed_url" ('https://www.youtube.com/embed...bJY0\n', '<p><amp-youtube data-videoid=...</p>\n', '<p><amp-youtube data-videoid=...</p>\n')
7) Test_AMP_Validation_Manager::test_decorate_shortcode_and_filter_source

Expected Behaviour

You shall not fail!

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