Update stale workflow: remove trigger on comments and explicit permissions

[echoix]

Proposed Changes

1. Triggering on each issue/pr comment isn’t used anymore, dates back to 2021.
2. Add explicit permissions, as recommended in https://github.com/actions/stale/tree/03af7c36d33f4905e618fac0a1bb7e6d05f0d41b#recommended-permissions

Readiness Checklist

Author/Contributor

• Add entry to the CHANGELOG listing the change and linking to the corresponding issue (if appropriate)
• If documentation is needed for this change, has that been included in this pull request

Reviewing Maintainer

• Label as breaking if this is a large fundamental change
• Label as either automation, bug, documentation, enhancement, infrastructure, or performance

[echoix]

🦙 MegaLinter status: ⚠️ WARNING

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See detailed report in MegaLinter reports

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[echoix]

I wanted to report this last Easter, but didn't get to it yet. It's in the same idea of #2614, reducing unneeded workflow runs when nothing is done.

[nvuillam]

thanks for the PR @echoix :)

[nvuillam]

great !