Support for Wagtail 2.11 release

[Stormheg]

Hi 👋

This PR adds support for the latest Wagtail 2.11 release.

A new 1.4.0 1.3.0 release of this package should be made to PyPi.

[Stormheg]

Regarding the failing CI:

coveralls.exception.CoverallsException: Running on Github Actions but GITHUB_TOKEN is not set. Add "env: GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}" to your step config.

Looks like Coveralls now expects to be passed GITHUB_TOKEN. I'll try adding that and see if that works...

[Stormheg]

That didn't work...

coveralls.exception.CoverallsException: Could not submit coverage: 500 Server Error: Internal Server Error for url: https://coveralls.io/api/v1/jobs

[willbarton]

@Stormheg I'm trying to see what might be going on with Coveralls here.

[coveralls]

Pull Request Test Coverage Report for Build 391900251

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 232896458:	0.0%
Covered Lines:	202
Relevant Lines:	202

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💛 - Coveralls

[Stormheg]

@willbarton thanks, coveralls is working now!

[willbarton]

Thanks, @Stormheg!