changelog bot: commit as last commit author

[dsokal]

Checklist

• I've added an entry to CHANGELOG.md if necessary. You can comment this pull request with /changelog-entry [breaking-change|new-feature|bug-fix|chore] [message] and CHANGELOG.md will be updated automatically.
• I've tagged the changelog entry with [EAS BUILD API] if it's a part of a breaking change to EAS Build API (only possible when updating @expo/eas-build-job package).

Why

Follow up to #676
I've realized that if we commit as @expo-ci then this user appears as the co-author of the commit when the PR gets merged.

How

Commit CHANGELOG.md changes as the last PR commit author.

Test Plan

Tested in the forked repo - https://github.com/dsokal/eas-cli/commits/main

Compare the first and the other merge commit:

[github-actions]

Size Change: -47 B (0%)

Total Size: 22.5 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	22.5 MB	-47 B (0%)

_{compressed-size-action}