chore(csharp): Bump System.Text.Json from 9.0.9 to 9.0.12

---
updated-dependencies:
- dependency-name: System.Text.Json
  dependency-version: 9.0.12
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

csharp/Directory.Packages.props

@@ -46,7 +46,7 @@
     <PackageVersion Include="System.Diagnostics.DiagnosticSource" Version="9.0.6" />
     <PackageVersion Include="System.Net.Http" Version="4.3.4" />
     <PackageVersion Include="System.Net.Http.WinHttpHandler" Version="8.0.2" />
-    <PackageVersion Include="System.Text.Json" Version="9.0.9" />
+    <PackageVersion Include="System.Text.Json" Version="9.0.12" />
     <PackageVersion Include="System.Threading.Channels" Version="9.0.8" />
     <PackageVersion Include="xunit" Version="2.9.3" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="3.1.5" />