Bump node-fetch from 2.6.0 to 2.6.7 in /scripts/gcb2slack

Bumps [node-fetch](https://github.com/node-fetch/node-fetch) from 2.6.0 to 2.6.7.
- [Release notes](https://github.com/node-fetch/node-fetch/releases)
- [Commits](node-fetch/node-fetch@v2.6.0...v2.6.7)

---
updated-dependencies:
- dependency-name: node-fetch
  dependency-type: indirect
...

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