ci: upload artifacts for language bindings

[pentamassiv]

The .Gir files are not committed to the repo. For me as a maintainer of language bindings this means I have to either wait for it to be packaged or build it myself to generate the bindings. I've added a step to upload the bindings to the workflow.

I also took the liberty to update the used actions. Github recommends to pin them with their commit. Otherwise malicious Action authors can force push a new tag with malicious code to infect the repo.

[wmww]

Makes sense.

1. Where does it upload them to? Do the new artifacts replace the previous ones or get tagged with the commit they were generated from or what?
2. Maybe move the job to the deploy_docs action? We probably want to do it when new code hits main instead of every time a PR is opened/pushed to.

[pentamassiv]

They get uploaded with the workflow. You can see how it works here: https://github.com/wmww/gtk4-layer-shell/actions/runs/18924171309

At the bottom of the page is the entry with the build artifacts. They don't replace anything. The size is small enough that there shouldn't be a problem to upload them for each run of the build workflow but of course you could also do it in the deploy_docs workflow.