Bump System.Collections.Immutable from 5.0.0 to 6.0.0

Bumps [System.Collections.Immutable](https://github.com/dotnet/runtime) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v5.0.0...v6.0.0)

---
updated-dependencies:
- dependency-name: System.Collections.Immutable
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

src/StreamJsonRpc/StreamJsonRpc.csproj

@@ -24,7 +24,7 @@
     <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
     <PackageReference Include="Microsoft.CodeAnalysis.PublicApiAnalyzers" Version="3.3.3" PrivateAssets="all" />
     <PackageReference Include="Nullable" Version="1.3.0" PrivateAssets="all" />
-    <PackageReference Include="System.Collections.Immutable" Version="5.0.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="6.0.0" />
     <PackageReference Include="System.Diagnostics.DiagnosticSource" Version="6.0.0" />
     <PackageReference Include="System.IO.Pipelines" Version="6.0.1" />
     <PackageReference Include="System.Memory" Version="4.5.4" />