[maintenance] E2E tests aren't running on Version Packages PR

[1000hz]

We use @changesets/action to open a PR that manages our versioning, which gets created/updated during a step of https://github.com/cloudflare/wrangler-action/blob/main/.github/workflows/release.yml. We also run our E2E tests via a workflow that runs on pull_request events. It turns out that GitHub avoids triggering workflows from events generated by other workflows when using the automatically provided GITHUB_TOKEN, which means E2E tests don't get triggered to run any time the Version Packages PR is opened or updated. Sad!

However, in late 2022 GitHub made an exception to allow workflows to be triggered via workflow_dispatch events even if GITHUB_TOKEN was used.

We should add a step to our release.yml workflow to send a workflow_dispatch event for the E2E workflow with a ref of changeset-release/main (following the example in the linked blog post above). We'll also need to ad a new on: workflow_dispatch trigger to our E2E workflow.