Use NpgsqlConnection when checking if database exists.

The NpgsqlRelationalConnection gets an implicit reference to the DbContext from the original connection (through Dependencies). That could tamper with the original DbContext's ServiceProvider when adding a connection to completly different pool. Also, the test only wants a connection to the database which NpgsqlConnection could provide.
CreateAdminConnection suffers from the same problem. That together with this may be the root of the problem of #3560.

Author: marcusber

src/EFCore.PG/Storage/Internal/INpgsqlRelationalConnection.cs

@@ -32,5 +32,5 @@ public interface INpgsqlRelationalConnection : IRelationalConnection
     ///     any release. You should only use it directly in your code with extreme caution and knowing that
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
-    ValueTask<INpgsqlRelationalConnection> CloneWith(string connectionString, bool async, CancellationToken cancellationToken = default);
+    ValueTask<NpgsqlConnection> CloneWith(string connectionString, bool async, CancellationToken cancellationToken = default);
 }

src/EFCore.PG/Storage/Internal/NpgsqlRelationalConnection.cs

@@ -232,7 +232,7 @@ public override Transaction? CurrentAmbientTransaction
     ///     any release. You should only use it directly in your code with extreme caution and knowing that
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
-    public virtual async ValueTask<INpgsqlRelationalConnection> CloneWith(
+    public virtual async ValueTask<NpgsqlConnection> CloneWith(
         string connectionString,
         bool async,
         CancellationToken cancellationToken = default)
@@ -241,13 +241,6 @@ public virtual async ValueTask<INpgsqlRelationalConnection> CloneWith(
             ? await DbConnection.CloneWithAsync(connectionString, cancellationToken).ConfigureAwait(false)
             : DbConnection.CloneWith(connectionString);
 
-        var relationalOptions = RelationalOptionsExtension.Extract(Dependencies.ContextOptions)
-            .WithConnectionString(null)
-            .WithConnection(clonedDbConnection);
-
-        var optionsBuilder = new DbContextOptionsBuilder();
-        ((IDbContextOptionsBuilderInfrastructure)optionsBuilder).AddOrUpdateExtension(relationalOptions);
-
-        return new NpgsqlRelationalConnection(Dependencies with { ContextOptions = optionsBuilder.Options }, dataSource: null);
+        return clonedDbConnection;
     }
 }