build(deps): bump third_party/yaml-cpp from `47d32aa` to `21d75fa`
build(deps): bump third_party/yaml-cpp from `47d32aa` to `21d75fa`

Bumps [third_party/yaml-cpp](https://github.com/jbeder/yaml-cpp) from `47d32aa` to `21d75fa`.
- [Release notes](https://github.com/jbeder/yaml-cpp/releases)
- [Commits](https://github.com/jbeder/yaml-cpp/compare/47d32aadf0ea026c2e76cf07c9d08a022048b0f7...21d75fa4cd6eb57af08e07053fe55ccab78a0e2f)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
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