Comment 8 for bug 1904906

Hi Daniel, yes, 5.8 is - as of today - still the current kernel in hirsute (main and proposed).
But the kernel teams plans to migrate to 5.10 soon, hence the effort (and pre-requirement for the migration) to test secureboot lock-down upfront. This is to make sure that potential issues in the secureboot lock-down area will not affect any (production) keys.
The keys used for signing are bound the the archive where the kernel is build and comes from, and the PPA has a separate one.
Inside of the PPA you will also find the 5.10 source code as tar.gz file.

If you follow this PPA link:
https://launchpad.net/~canonical-kernel-team/+archive/ubuntu/bootstrap/+packages
and click on the kernel that was used for the testing (and open the twistie or section), or at least on a kernel that is close enough (this these kernels get pretty frequently updated), like:
"linux-5.10 - 5.10.0-0.1",
you will find the sources in the (I think only) tar.gz file that is listed there, like:
linux-5.10_5.10.0-0.1.tar.gz (176.3 MiB)
https://launchpad.net/~canonical-kernel-team/+archive/ubuntu/bootstrap/+sourcefiles/linux-5.10/5.10.0-0.1/linux-5.10_5.10.0-0.1.tar.gz