Bump DiffPlex from 1.8.0 to 1.9.0

---
updated-dependencies:
- dependency-name: DiffPlex
  dependency-version: 1.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

ProjectDirector/ProjectDirector.csproj

@@ -2,7 +2,7 @@
 
 <Project Sdk="ktsu.Sdk.App/1.8.0">
   <ItemGroup>
-    <PackageReference Include="DiffPlex" Version="1.8.0" />
+    <PackageReference Include="DiffPlex" Version="1.9.0" />
     <PackageReference Include="ktsu.AppDataStorage" Version="1.15.9" />
     <PackageReference Include="ktsu.Extensions" Version="1.5.7" />
     <PackageReference Include="ktsu.ImGuiApp" Version="2.1.7" />