Use standard runners for issue triage framework jobs

[nagilson]

Summary

• keep roles: all; non-maintainer issue authors are already authorized
• run gh-aw framework jobs on ubuntu-latest instead of ubuntu-slim
• avoid the single-CPU runner's hard 15-minute job timeout canceling triage before any step executes

Root cause

The workflow did trigger for non-maintainer issue #55639 as actor damienhoneyford, but its pre_activation job never acquired a runner and was canceled after exactly 15 minutes with runner_id: 0, zero steps, and zero billable milliseconds:

https://github.com/dotnet/sdk/actions/runs/31119268940

GitHub documents that ubuntu-slim has a hard 15-minute job timeout:

https://docs.github.com/en/actions/reference/runners/github-hosted-runners#single-cpu-runners

The gh-aw documentation says roles: all allows any user and runs-on-slim controls generated framework jobs:

https://github.github.com/gh-aw/reference/triggers/
https://github.github.com/gh-aw/reference/frontmatter/

A separate fork test confirms the existing permissions work for a non-maintainer. Issue nagilson/sdk#128, opened by Toxitricity with author_association: NONE, automatically triggered and completed successfully:

https://github.com/nagilson/sdk/actions/runs/31130404269

Validation

gh aw compile issue-triage --strict completed with zero errors and zero warnings.

Fixes #55652

Live branch-ref validation: https://github.com/nagilson/sdk/actions/runs/31133889908 assigned pre_activation to the requested ubuntu-latest label and completed that job successfully.

[azure-pipelines]

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