Bump FSharp.SystemTextJson from 1.2.42 to 1.3.13

Bumps [FSharp.SystemTextJson](https://github.com/tarmil/FSharp.SystemTextJson) from 1.2.42 to 1.3.13.
- [Release notes](https://github.com/tarmil/FSharp.SystemTextJson/releases)
- [Changelog](https://github.com/Tarmil/FSharp.SystemTextJson/blob/master/CHANGELOG.md)
- [Commits](Tarmil/FSharp.SystemTextJson@v1.2.42...v1.3.13)

---
updated-dependencies:
- dependency-name: FSharp.SystemTextJson
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

src/Tests/Tests.fsproj

@@ -35,7 +35,7 @@
     <Compile Include="Misc.fs" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="FSharp.SystemTextJson" Version="1.2.42" />
+    <PackageReference Include="FSharp.SystemTextJson" Version="1.3.13" />
     <PackageReference Include="FsUnit" Version="5.6.1" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
     <PackageReference Include="NUnit" Version="3.14.0" />