[CI] Investigate why the issue comments trigger cmd bot and waste CI runners

[bkontur]

#954 is just an issue and at least last two cmd jobs here:

were triggered by issue comments:
https://github.com/polkadot-fellows/runtimes/actions/runs/18405286775
https://github.com/polkadot-fellows/runtimes/actions/runs/18405704578

Probably related to the:

name: Command

on:
  issue_comment: # listen for comments on issues
    types: [created]

And needs some more IF-ing?

if: ${{ startsWith(github.event.comment.body, '/cmd') ...

[bkchr]

We need this: https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows#issue_comment-on-issues-only-or-pull-requests-only

So yes, more IFING!!! IFING!! IFING