chore: avoid update-docs workflow runs on pushes to main

[npalm]

Docs should be updated on branches, in case of the locked main branch a PR is created. This to ensure the main is up-to-date.

[koendelaat]

I think there are two options to handle update-docs on the main branch

1. Don't update docs on the main branch
2. Create a PR when docs need to be updated on the main branch

Current suggestion seems to implement both options at the same time, which makes no sense to me. So we either have to skip checking on the main branch (as suggested), but then we should also remove the conditional PR creation step.

Other option could be to fix the PR creation step.
Suggestion:

      - name: Create Pull Request (main branch only)
        if: github.ref == 'refs/heads/main'
        uses: peter-evans/create-pull-request@153407881ec5c347639a548ade7d8ad1d6740e38 # ratchet:peter-evans/create-pull-request@v5.0.2
        with:
          token: ${{ steps.token.outputs.token || secrets.GITHUB_TOKEN }}
          commit-message: "Update Terraform docs"
          title: "docs: Update Terraform docs"
          branch: update-docs
          base: ${{ github.ref }}

[npalm]

@koendelaat thx. Updated the workflow. The workflow should now run on any branch in any repo and commit changes. With only an exception for the main branch in this repo. In that case a PR should be opened.