Initially run update-changelogs only for non-draft PRs (MetaMask#8750)

## Explanation

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When an engineer opens a release PR, they may want to make additional
changes to the release plan before they are ready to open the PR, and so
they may not want to populate dependency bump entries across changelogs
right away. To account for this, this commit modifies the
`update-changelogs` workflow so that the initial run only occurs if the
PR is created in non-draft status or is taken out of draft otherwise.

## References

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Are there client or consumer pull requests to adopt any breaking
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* Fixes #12345
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## Checklist

- [ ] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [ ] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/processes/updating-changelogs.md)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/processes/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk workflow gating change; it only adjusts when the GitHub
Actions job runs and does not affect production code paths.
> 
> **Overview**
> Updates the `update-changelogs` GitHub Actions workflow to **not run
automatically for draft PRs**.
> 
> The workflow now triggers on `pull_request_target` `ready_for_review`
and tightens the `is-fork` job condition so the initial run only occurs
when the PR is *not* a draft (while still allowing manual runs via
`@metamaskbot update-changelogs` comments).
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
f8a1fc0. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: mcmire

.github/workflows/update-changelogs.yml

@@ -9,6 +9,7 @@ on:
       - main
     types:
       - opened
+      - ready_for_review
 
 permissions:
   contents: write
@@ -17,7 +18,7 @@ permissions:
 jobs:
   is-fork:
     name: Determine whether this PR is from a fork
-    if: github.event_name == 'pull_request_target' || (github.event.issue.pull_request && startsWith(github.event.comment.body, '@metamaskbot update-changelogs'))
+    if: (github.event_name == 'pull_request_target' && !github.event.pull_request.draft) || (github.event.issue.pull_request && startsWith(github.event.comment.body, '@metamaskbot update-changelogs'))
     runs-on: ubuntu-latest
     outputs:
       is-fork: ${{ steps.is-fork.outputs.is-fork }}