Merge current upstream PETSc about firedrake

[dham]

That's a shocking oversight on my part which I have just remedied. You should now have an invite giving you push access to the various Firedrake repos.

[dham]

The mechanism for getting the PETSc fork updated is:

1. Push a branch to firedrake's PETSc fork with upstream master merged in.
2. Push a branch to firedrake with build.yaml modified to use the PETSc branch above.
3. Open a draft PR on the firedrake branch so that the CI runs.

If the CI runs successfully, we can update.

[connorjward]

We have written down the procedure in more detail here.

[angus-g]

Thanks both, I guess the only issue here is the assumption that one has commit access to the firedrakeproject versions of this repository. I could submit a PR that modifies requirements-git.txt to point to my fork, although I guess the workflows would also need to be approved to run here anyway?

[angus-g]

Thanks @dham! All seems to be underway now.