CompatHelper: bump compat for DomainSets in [extras] to 0.8, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the DomainSets package from 0.7.15 to 0.7.15, 0.8.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.50%. Comparing base (d5e7c71) to head (fc76467).

❗ There is a different number of reports uploaded between BASE (d5e7c71) and HEAD (fc76467). Click for more details.

HEAD has 3 uploads less than BASE

Flag	BASE (d5e7c71)	HEAD (fc76467)
docs	2	1
	2	0

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #205       +/-   ##
===========================================
- Coverage   82.48%   48.50%   -33.98%     
===========================================
  Files          19       18        -1     
  Lines        1895     1876       -19     
===========================================
- Hits         1563      910      -653     
- Misses        332      966      +634     

Flag	Coverage Δ
docs	48.50% <ø> (ø)

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