Bump System.Text.Json (#19)

Bumps [System.Text.Json](https://github.com/dotnet/runtime) from 6.0.0-preview.5.21254.9 to 6.0.0-preview.5.21255.7.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](https://github.com/dotnet/runtime/commits)

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src/GitBuildInfo.SourceGenerator.csproj

@@ -42,7 +42,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.10.0-3.21254.9" />
     <PackageReference Include="Nullable" Version="1.3.0" />
-    <PackageReference Include="System.Text.Json" Version="6.0.0-preview.5.21254.9" />
+    <PackageReference Include="System.Text.Json" Version="6.0.0-preview.5.21255.7" />
   </ItemGroup>
 
   <Import Project="$(MSBuildProjectName).targets" />

tests/GitBuildInfo.SourceGenerator.Tests.csproj

@@ -7,7 +7,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.10.0-3.21254.9" />
-    <PackageReference Include="System.Text.Json" Version="6.0.0-preview.5.21254.9" />
+    <PackageReference Include="System.Text.Json" Version="6.0.0-preview.5.21255.7" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.8.3" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">