Bump nodemailer from 6.7.0 to 6.9.15

Bumps [nodemailer](https://github.com/nodemailer/nodemailer) from 6.7.0 to 6.9.15.
- [Release notes](https://github.com/nodemailer/nodemailer/releases)
- [Changelog](https://github.com/nodemailer/nodemailer/blob/master/CHANGELOG.md)
- [Commits](nodemailer/nodemailer@v6.7.0...v6.9.15)

---
updated-dependencies:
- dependency-name: nodemailer
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>