Bump System.Text.Json from 6.0.0 to 8.0.4 in /src/Dahomey.Json

Bumps System.Text.Json from 6.0.0 to 8.0.4.

---
updated-dependencies:
- dependency-name: System.Text.Json
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

src/Dahomey.Json/Dahomey.Json.csproj

@@ -25,7 +25,7 @@
 
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <PackageReference Include="System.Collections.Immutable" Version="6.0.0" />
-    <PackageReference Include="System.Text.Json" Version="6.0.0" />
+    <PackageReference Include="System.Text.Json" Version="8.0.4" />
     <PackageReference Include="Nullable" Version="1.3.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>