CI: Use regular solver for docker build

[phofl]

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[phofl]

Newest numpy and numba are incompatible, so the docker build fails without taking dependencies into account

[MarcoGorelli]

thanks @phofl

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 1.5.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 083d030d473260456dabd7d4fd924830e557d97a

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #50341: CI: Use regular solver for docker build'

4. Push to a named branch:

git push YOURFORK 1.5.x:auto-backport-of-pr-50341-on-1.5.x

5. Create a PR against branch 1.5.x, I would have named this PR:

"Backport PR #50341 on branch 1.5.x (CI: Use regular solver for docker build)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

[MarcoGorelli]

the dockerfile in 1.5.x is very different, does this need backporting?

[phofl]

Wasn't aware of that, are we using mamba there? If yes, then we don't have to backport

[MarcoGorelli]

yup

[MarcoGorelli]

we've backported the docker changes, so let's backport this too

@meeseeksdev please backport to 1.5.x