Add support for pnpm/action-setup with version: updates

[alexfaxe]

Tell us more.

Similar to the recent feature addition done in #34658

The github-actions manager should be updated to extract the version value when using pnpm/action-setup.

Example syntax:

- name: Setup pnpm
      uses: pnpm/action-setup@v4
      with:
        version: 10.6.1

[rarkins]

What is the datasource and packageName to be used to look up valid versions? e.g. is it based on the pnpm package on registry.npmjs.org or something else?

[alexfaxe]

In the repo where I noticed the discrepancy the version was updated properly within mise.toml and also in the packageManager part of the package.json.

So whichever datasource and packageName is being used in those handlers should also be fine here.

[rarkins]

There are multiple ways to install pnpm, not all may be in sync. We should try to find out exactly which this action uses

[rarkins]

I think it's here: https://github.com/pnpm/action-setup/blob/a7487c7e89a18df4991f7f222e4898a00d66ddda/src/install-pnpm/run.ts#L23-L24

So we can probably use the datasource npm and packageName of pnpm

[rarkins]

Converted to issue: #34767