build(deps): bump form-data in /.github/workflows/scripts/mailchimp

Bumps [form-data](https://github.com/form-data/form-data) from 2.5.1 to 2.5.5.
- [Release notes](https://github.com/form-data/form-data/releases)
- [Changelog](https://github.com/form-data/form-data/blob/v2.5.5/CHANGELOG.md)
- [Commits](form-data/form-data@v2.5.1...v2.5.5)

---
updated-dependencies:
- dependency-name: form-data
  dependency-version: 2.5.5
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]