Bump to @actions/cache v4 to fix caching failures

[agriyakhetarpal]

This shall fix #47. The linked issue has more details; the gist is that actions/cache v3 is deprecated and GitHub has advised users and Actions authors to move to v4 to fix builds.

[agriyakhetarpal]

The tests ran in a PR on my fork (agriyakhetarpal#1), and have passed as well: https://github.com/agriyakhetarpal/setup-emsdk/actions/runs/15252190352/job/42891431540?pr=1, where I had temporarily changed the workflows to adjust this. I've put some suggestions below in my self-review to undo them:

[agriyakhetarpal]

2.0.20 is a bit too old by now, would it be okay to have bumped to 4.0.9?

[agriyakhetarpal]

Hi @mymindstorm, would you be able to review this PR in the near future? Currently, setting up Emscripten takes three minutes on all workflow runs due to the obsolete @actions/cache v3, which has been declared to be no longer functional. It would be beneficial to all users if you could allocate the necessary bandwidth to review this PR and release it soon after. Thank you, a lot, for your time and work!

I will be creating a friendly fork under the @pyodide organisation in the meantime to use this action to speed up builds. I shall archive it as soon as you return to active development on this repository, I promise! :)

[agriyakhetarpal]

Hi @mymindstorm and to those subscribed to this PR: I created a friendly fork at https://github.com/pyodide/setup-emsdk/ and a corresponding release at https://github.com/pyodide/setup-emsdk/releases/tag/v15 for our use, which directs to this repository for accreditation. It will be archived once this PR is merged and included in a release.

It can be used by swapping out the actions from

- uses: mymindstorm/setup-emsdk@v14

to

- uses: pyodide/setup-emsdk@v15

[bdon]

@agriyakhetarpal confirming the fork worked, thanks for publishing!

[Danil42Russia]

@mymindstorm, hello! Can you view this request?

[agriyakhetarpal]

Thanks @Danil42Russia, good catch!