Bump node-fetch from 2.6.0 to 2.6.7 in /scripts/gcb2slack (#2866)

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
...

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Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]