nuget-dressca: bump NSwag.MSBuild in /samples/Dressca/dressca-backend

Bumps [NSwag.MSBuild](https://github.com/RicoSuter/NSwag) from 13.19.0 to 13.20.0.
- [Release notes](https://github.com/RicoSuter/NSwag/releases)
- [Changelog](https://github.com/RicoSuter/NSwag/blob/master/CHANGELOG.md)
- [Commits](RicoSuter/NSwag@v13.19.0...v13.20.0)

---
updated-dependencies:
- dependency-name: NSwag.MSBuild
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

samples/Dressca/dressca-backend/Directory.Packages.props

@@ -12,7 +12,7 @@
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.7.0" />
     <PackageVersion Include="Moq" Version="4.20.69" />
     <PackageVersion Include="NSwag.AspNetCore" Version="13.19.0" />
-    <PackageVersion Include="NSwag.MSBuild" Version="13.19.0" />
+    <PackageVersion Include="NSwag.MSBuild" Version="13.20.0" />
     <PackageVersion Include="StyleCop.Analyzers" Version="1.2.0-beta.507" />
     <PackageVersion Include="xunit" Version="2.5.0" />
     <PackageVersion Include="xunit.abstractions" Version="2.0.3" />