Add workflow for updating pnpm packages

[csc-felipe]

Description

Dependabot doesn't update pnpm packages, so here's an action to create a PR with pnpm updates.

It's not perfect, though.

1. It runs when a new PR is created, as cron jobs only run on the default branch
2. It uses GITHUB_TOKEN, so the new PR doesn't trigger other workflows
3. PR has to be closed and opened again to run checks

More info:

• https://docs.github.com/en/actions/using-workflows/triggering-a-workflow#triggering-a-workflow-from-a-workflow
• https://github.com/peter-evans/create-pull-request/blob/main/docs/concepts-guidelines.md#triggering-further-workflow-runs
• https://github.com/peter-evans/create-pull-request/blob/main/docs/examples.md#use-case-create-a-pull-request-to-update-x-periodically

Related issues

Type of change

• New feature (non-breaking change which adds functionality)

Changes Made

• Added a new github workflow for automatically updating pnpm packages
• Change workflows from push to pull_request, so that checks run in the automated PR

Testing

• Tests do not apply

Mentions

[csc-felipe]

It seems to work: #1002

[csc-felipe]

Not all the checks in that PR are running 🤔

[csc-felipe]

I'm thinking that those checks might need to have on: pull_request as well.

[csc-felipe]

It seems to work if the workflows have on: pull_request. But the generated PR will only work after this is merged to devel, as it changes push to pull_request in workflows.