Cover the configuration change publishing filter with its test

The Castle Siege persistence import (#860) brought
EntityFrameworkContextBase.PublishesConfigurationChanges into the tree,
but not the test which pins its behaviour, and not the guard which keeps
the two initialization test fixtures from configuring the connection
twice.

Add both, unchanged from upstream.

tests/MUnique.OpenMU.Persistence.Initialization.Tests/JsonQueryBuilderTests.cs

@@ -24,7 +24,10 @@ internal class JsonQueryBuilderTests
     [OneTimeSetUp]
     public void Setup()
     {
-        ConnectionConfigurator.Initialize(new ConfigFileDatabaseConnectionStringProvider());
+        if (!ConnectionConfigurator.IsInitialized)
+        {
+            ConnectionConfigurator.Initialize(new ConfigFileDatabaseConnectionStringProvider());
+        }
     }
 
     /// <summary>