test: drop Microsoft.EntityFrameworkCore.InMemory dependency

All tests now run against a real MariaDB via Testcontainers (TestBaseSetup),
matching production behaviour for unique constraints, transactions, and
referential integrity.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: renemadsen

eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn.Test/TimePlanning.Pn.Test.csproj

@@ -7,7 +7,6 @@
     </PropertyGroup>
 
     <ItemGroup>
-      <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="10.0.5" />
       <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
       <PackageReference Include="Google.Protobuf" Version="3.34.1" />
       <PackageReference Include="Grpc.Net.Client" Version="2.76.0" />