Update Orm/Xtensive.Orm/Orm/Entity.cs

Co-authored-by: Alexey Kulakov <alexey.kulakov@dataobjects.net>

Author: SergeiPavlov

Orm/Xtensive.Orm/Orm/Entity.cs

@@ -288,7 +288,7 @@ public void IdentifyAs(EntityIdentifierType identifierType)
         return;
       switch (identifierType) {
       case EntityIdentifierType.Auto:
-        string identifier = $"#{operations.GetNextIdentifier().ToString("0000")}";
+        string identifier = operations.GetNextIdentifier().ToString("\\#0000");
         operations.RegisterEntityIdentifier(Key, identifier);
         break;
       case EntityIdentifierType.None: