Vulnerability in a sub-dependency (form-data) in @slack/wehooks@7.0.5

`@slack/wehooks@7.0.5` package includes a dependency `form-data@4.0.3`. 

The package is labeled as a vulnerability. See more information here: https://github.com/form-data/form-data/security/advisories/GHSA-fjxv-7rqg-78g4. 
Could you make the necessary changes?

#### Packages:

- [x] `@slack/webhooks`
