build(deps): bump Microsoft.AspNetCore.OpenApi in /tests/DemoApi.Tests

Bumps [Microsoft.AspNetCore.OpenApi](https://github.com/dotnet/aspnetcore) from 9.0.2 to 9.0.4.
- [Release notes](https://github.com/dotnet/aspnetcore/releases)
- [Changelog](https://github.com/dotnet/aspnetcore/blob/main/docs/ReleasePlanning.md)
- [Commits](dotnet/aspnetcore@v9.0.2...v9.0.4)

---
updated-dependencies:
- dependency-name: Microsoft.AspNetCore.OpenApi
  dependency-version: 9.0.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

src/DemoApi/DemoApi.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="9.0.2" />
+    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="9.0.4" />
   </ItemGroup>
 
 </Project>