Bump System.Collections.Immutable from 8.0 to 9.0.1

Bumps [System.Collections.Immutable](https://github.com/dotnet/runtime) from 8.0 to 9.0.1.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v8.0.0...v9.0.1)

---
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>

Author: dependabot[bot]

src/Foundatio.Xunit/Foundatio.Xunit.csproj

@@ -7,7 +7,7 @@
     <ProjectReference Include="..\Foundatio\Foundatio.csproj" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="System.Collections.Immutable" Version="8.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="9.0.1" />
     <PackageReference Include="Microsoft.Extensions.Logging" Version="8.0" />
     <PackageReference Include="xunit" Version="2.9.3" />
   </ItemGroup>