build(deps): bump form-data from 2.5.5 to 2.5.6 in /site

Bumps [form-data](https://github.com/form-data/form-data) from 2.5.5 to 2.5.6.
- [Release notes](https://github.com/form-data/form-data/releases)
- [Changelog](https://github.com/form-data/form-data/blob/master/CHANGELOG.md)
- [Commits](form-data/form-data@v2.5.5...v2.5.6)

---
updated-dependencies:
- dependency-name: form-data
  dependency-version: 2.5.6
  dependency-type: indirect
...

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

Author: dependabot[bot]