Update serde_yaml requirement from 0.8.24 to 0.9.19

[dependabot[bot]]

Updates the requirements on serde_yaml to permit the latest version.

Release notes

Sourced from serde_yaml's releases.

0.9.19

• Fix message duplication between serde_yaml::Error's Display and source() (#359, #360)

Commits

• 4e1cbd8 Release 0.9.19
• f351fc7 Merge pull request #360 from dtolnay/errorsource
• f27e4c5 Fix message duplication between error Display and source()
• fc039c6 Refer to std::error::Error trait as StdError
• 7f1db12 Release 0.9.18
• 248d6de Merge pull request #358 from dtolnay/unicode
• 779f016 Update U+1F389 test
• 12b48b5 Pull in Unicode high codepoints fix from unsafe-libyaml 0.2.7
• b6f6957 Add test of Unicode larger than U+FFFF
• eac69a2 Merge pull request #357 from dtolnay/stringescape
• Additional commits viewable in compare view

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