Go version from go.mod file - extra maintenance and possible version drift, user error

In a consumer of this workflow there are three places to update the Go version:

* `go.mod` - ensures local development uses the right version - https://github.com/crossplane-contrib/provider-kubernetes/blob/main/go.mod#L3
* `ci` - https://github.com/crossplane-contrib/provider-kubernetes/blob/main/.github/workflows/ci.yml#L13 (not using the reusable workflow in this case, but if it did it would still need the version)
* `publish` - the version used when building a release. It's _also_ a manual input. https://github.com/crossplane-contrib/provider-kubernetes/blob/main/.github/workflows/publish-provider-package.yaml#L10-L12

I propose moving to `go-version-file` instead as the default, and removing the input from the publish workflow in provider-kubernetes.

```yaml
- uses: actions/setup-go@v5
with:
go-version-file: 'go.mod'
```

https://github.com/actions/setup-go?tab=readme-ov-file#getting-go-version-from-the-gomod-file

This will ensure there's a single place to update the version, and that they all operate on the same version number.

Start with the referenced go.mod, .github/workflows/ci.yml, and .github/workflows/publish-provider-package.yaml files, then compare how each currently receives the Go version. Update the workflow configuration so the version comes from go.mod and remove the publish workflow's manual version input. Done means local, CI, and release builds use one version source.

Written by the indexing model from the issue text.