Fix potentially privileged pull request medium query

[JarLob]

No description provided.

[Copilot]

Pull Request Overview

This PR fixes the handling of pull request code injection alerts by updating the associated configuration files and change notes.

• Updated change notes to document the fix for the pull_request medium query.
• Modified externally_triggereable_events.yml to include the "pull_request" event.
• Updated context_event_map.yml with mappings for the "pull_request" event.

Reviewed Changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated no comments.

File	Description
actions/ql/lib/change-notes/released/2025-03-20-pullrequest.md	Adds a release note for the pull_request medium query fix
actions/ql/lib/ext/config/externally_triggereable_events.yml	Adds the "pull_request" event to the externally triggereable events list
actions/ql/lib/ext/config/context_event_map.yml	Adds mappings for the "pull_request" event to the context event map

Files not reviewed (2)

• actions/ql/test/query-tests/Security/CWE-094/CodeInjectionCritical.expected: Language not supported
• actions/ql/test/query-tests/Security/CWE-094/CodeInjectionMedium.expected: Language not supported

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[adityasharad]

Looks reasonable, one change note suggestion.

Is there a reason we didn't include these to begin with - were they considered trusted?

[JarLob]

Workflows are considered running without permissions and secrets when pull_request is triggered from a fork. But they run privileged when triggered from branches in the same repository. It is trusted because creation of a branch requires the contributor to have write permissions to the repository already.
Previously there was an attack vector when non-maintainer could create a pull request between branches in the target repository he don't own to exploit the injection. Now it is allowed to maintainers only. But overall I think it is better to fix injections always. This is what the medium query is about, it explicitly checks inNonPrivilegedContext.

[JarLob]

Please merge. I don't have the permission.