update github actions to get rid of deprecation warnings

[mgor]

update versions to get rid of:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3, actions/setup-python@v4, actions/cache@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

also includes actions/setup-node@v3 and borales/actions-yarn@v3

with actions/cache@v3 on windows image there would be an error, but the step wouldn't fail:

[Windows](https://github.com/mgor/locust/actions/runs/9692188762/job/26745040620#step:6:14)
Input required and not supplied: path

when updating to actions/cache@v4 the step would also fail. to fix this the shell for the steps that redirects output to $GITHUB_{OUTPUT,ENV} was set to bash. since the default shell for windows runners is powershell, and echo ... >> ... isn't crossplatform compatible, and bash is available on the windows images.

[mgor]

not sure why py39 fails in print stats tests... saw that once in my other PR as well, but re-running it and it passed. doesn't seems like i have permission to re-run jobs though.

[cyberw]

I re-ran it now. Is it always 3.9? I was already eager to drop 3.9 support to use nice language features that were introduced in 3.10 :P

But I might not want to merge this right now - #2725 is quite a big change and I'd rather not make two changes in the build in the same release. For this reason I'm putting it in draft for now. Or is it urgent for you?

[mgor]

the two times i've seen it fail it was py39, doesn't really have any good statistics for it :)

no, not urgent at all, it's just that i hate warning/errors and wanted it fixed ;) so that's fine