Bump signet from 0.12.0 to 0.13.0
Bump signet from 0.12.0 to 0.13.0

Bumps [signet](https://github.com/google/signet) from 0.12.0 to 0.13.0.
- [Release notes](https://github.com/google/signet/releases)
- [Changelog](https://github.com/googleapis/signet/blob/master/CHANGELOG.md)
- [Commits](https://github.com/google/signet/compare/signet/v0.12.0...signet/v0.13.0)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
coderdojo-japan/coderdojo.jp,yasslab/coderdojo.jp,yasslab/coderdojo.jp,coderdojo-japan/coderdojo.jp,yasslab/coderdojo.jp,coderdojo-japan/coderdojo.jp,coderdojo-japan/coderdojo.jp