chore: Fix invalid PR number in eth-block-tracker changelog (#6881)

## Explanation

The `eth-block-tracker` changelog accidentally contained an invalid PR
number, which has been fixed in this PR.

## References

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Are there other links that reviewers should consult to understand these
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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/contributing.md#updating-changelogs),
highlighting breaking changes as necessary
- [ ] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Corrects PR numbers in `packages/eth-block-tracker/CHANGELOG.md` from
#7930 to #6865 for the Node.js minimum version change and monorepo
migration notes.
> 
> - **Changelog (`packages/eth-block-tracker/CHANGELOG.md`)**:
>   - Correct PR references from `#7930` to `#6865` for:
>     - The breaking change updating minimum Node.js version
>     - The migration to the `MetaMask/core` monorepo
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
caf93c0. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: Mrtenz

packages/eth-block-tracker/CHANGELOG.md

@@ -9,9 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
-- **BREAKING:** Update minimum Node.js version from `^18.16.0` to `^18.18.0` ([#7930](https://github.com/MetaMask/core/pull/7930))
+- **BREAKING:** Update minimum Node.js version from `^18.16.0` to `^18.18.0` ([#6865](https://github.com/MetaMask/core/pull/6865))
 - This package was migrated from `MetaMask/eth-block-tracker` to the
-  `MetaMask/core` monorepo ([#7930](https://github.com/MetaMask/core/pull/7930))
+  `MetaMask/core` monorepo ([#6865](https://github.com/MetaMask/core/pull/6865))
   - See [`MetaMask/eth-block-tracker`](https://github.com/MetaMask/eth-block-tracker/blob/main/CHANGELOG.md)
     for the original changelog.