Stats tracking code missing from AMP pages since 6.2

[danjjohnson]

Steps to reproduce the issue

1. Create a test site with Jetpack 6.1.1
2. Connect Jetpack and enable stats.
3. Install the AMP plugin: https://wordpress.org/plugins/amp/
4. Publish a post.
5. View the source code of the /amp/ version of a post. See the tracking code starting with <amp-pixel
6. Upgrade to Jetpack 6.2
7. View the source code again.

What I expected

The stats tracking code should still be there.

What happened instead

It's not there.

Reported in 1210111-zen

[kraftbj]

This is because the AMP plugin was updated to back off of adding JP support in 6.2: ampproject/amp-wp@c280a51

Jetpack is checking for amp_is_canonical : 1bd4eaa#diff-f26e9ed01c2ca4e906e59c7c15b45ab1R69

That function, though, is to check if themes are declaring their own AMP support, thus short-circuiting the default templates: https://github.com/Automattic/amp-wp/blob/6e6275b84bba131010a90dbea4d325986728057b/amp.php#L274

EDIT: #9625 looks like it should have addressed this, so might be something else. No joy nevertheless for a pixel in amp.

[anaemnesis]

I think I may have come across a site experiencing behaviour related to this in #1208872-zen.

Tracking code is present on non-AMP pages, but missing on AMP pages, which is causing stats from Twitter to not report correctly in Calypso.