Duplicate video URLs on WP 5.7 About screen

[SergeyBiryukov]

Reported by @mihdan on Russian WP Slack.

The About page for 5.7 has duplicate video URLs:

<div class="column about__image">
	<video controls>
		<source src="https://s.w.org/images/core/5.7/about-57-drag-drop-image.mp4" type="video/mp4" />
		<source src="https://s.w.org/images/core/5.7/about-57-drag-drop-image.mp4" type="video/webm" />
	</video>
</div>

I think the second URL is supposed to link to about-57-drag-drop-image.webm.

[audrasjb]

Given the webm video is actually available on w.org, we just need to change the URL.

[SergeyBiryukov]

In 50518:

Help/About: Correct the WebM video URL on About page.

Props mihdan, audrasjb.
Fixes #52756.

[SergeyBiryukov]

In 50519:

Help/About: Correct the WebM video URL on About page.

Props mihdan, audrasjb.
Merges [50518] to the 5.7 branch.
Fixes #52756.