chore: use self-hosted GitHub Actions runners

[superkindhq]

This PR updates all GitHub Actions workflows to use self-hosted runners.\n\nThe change replaces runs-on: ubuntu-* with runs-on: [self-hosted] to leverage self-hosted runners.

[Uzair-Ahmed-Dahraj]

Closing without merging. The change brings no benefit, and it breaks the fork's CI.

1. It saves nothing. GitHub's billing docs say: "GitHub Actions usage is free for self-hosted runners and for public repositories that use standard GitHub-hosted runners." This fork is public, so the hosted runners already cost nothing.
https://docs.github.com/en/billing/concepts/product-billing/github-actions

2. No runner picks up the jobs. This PR's own check job asked for the self-hosted label, and no runner took it:

• runner assigned: none
• queued: 2026-08-21 05:31 UTC
• cancelled: 2026-08-22 05:31 UTC, after 24 hours

After a merge, every workflow on the fork would wait and then fail in the same way.

3. GitHub advises against self-hosted runners on public repositories: "Self-hosted runners should almost never be used for public repositories on GitHub, because any user can open pull requests against the repository and compromise the environment." If someone later registers a runner, any fork PR could run code on that machine and reach its secrets and the GITHUB_TOKEN.
https://docs.github.com/en/actions/reference/security/secure-use

4. The PR does not need to touch the workflow files. These 8 workflows run only for PRs inside this fork. The CI for the Cloudflare submission (cloudflare#1075) runs in cloudflare/templates on Cloudflare's runners, so this change has no effect on the submission. The internal PR #3 already passed on GitHub's hosted runners.