Update 3rd-party Video Unit Tests to use more permanent videos

[garrett-eclipse]

This is a follow-up ticket from a discussion on slack, ticket in meta and associated core ticket #46986. To answer, what videos to use in unit tests for vimeo and youtube.

I'll quote the meta response from @dd32 as I feel it the most appropriate path forward;

Instead of using WordPress test accounts, could we instead fall back onto using a video uploaded by the embed company instead?

For example, for Vimeo, anything from Vimeo Staff ​https://vimeo.com/staff or the test video from ​https://player.vimeo.com/embed should be safe to use going forward. edit: The player embed page actually has a bunch of test videos with various states, such as not-embeddable, hosted by official vimeo test accounts, seems perfect for this use-case.

Having official WordPress accounts for every embed platform is not going to be viable from a management perspective IMHO, and having accounts everywhere with only a single W logo video doesn't lead to a super great experience when it ends up in search results.

Where WordPress does have a use for the service (Such as Youtube) using one of our uploads such as a ​release video does make sense though.

This ticket is to update those urls to use the youtube suggested video and the one from the Vimeo embed tutorial.
Youtube - ​https://www.youtube.com/watch?v=72xdCU__XCk
Vimeo - ​https://vimeo.com/76979871

[garrett-eclipse]

Initial patch to bring consistency to the vimeo/youtube urls used for tests.

[garrett-eclipse]

Note: While creating the patch I found some instances in Gutenberg so once this gets some review we can look to also bring consistency to those tests too.

[Mista-Flo]

Hey Garrett, nice one!

I have run the unit tests with the patch applied and it works, no regression.

[garrett-eclipse]

Awesome, let's get a committers review and see if we can land this in 5.6.

[SergeyBiryukov]

In 49117:

Tests: Update third-party video URLs in unit tests with more permanent videos.

This brings some consistency to the YouTube and Vimeo URLs used for tests:

• For YouTube, use the video of WordPress 5.0 release.
• For Vimeo, use one of the official test videos.

Props garrett-eclipse, dd32.
Fixes #51487. See ​#meta5467.

[garrett-eclipse]

Thanks @SergeyBiryukov I've added a note to the Automated Testing document here;
​https://make.wordpress.org/core/handbook/testing/automated-testing/