Ensure string.Join is not translated with non array-mapped param (#3105)

string.Join translations are just valid if their parameter's TypeMapping is NpgsqlArrayTypeMapping.

Author: georg-jung

src/EFCore.PG/Query/ExpressionTranslators/Internal/NpgsqlStringMethodTranslator.cs

@@ -1,5 +1,6 @@
 using Npgsql.EntityFrameworkCore.PostgreSQL.Query.Expressions.Internal;
 using Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.Mapping;
 using static Npgsql.EntityFrameworkCore.PostgreSQL.Utilities.Statics;
 using ExpressionExtensions = Microsoft.EntityFrameworkCore.Query.ExpressionExtensions;
 
@@ -339,7 +340,8 @@ public NpgsqlStringMethodTranslator(NpgsqlTypeMappingSource typeMappingSource, I
                 || method == String_Join4
                 || method == String_Join5
                 || method.IsClosedFormOf(String_Join_generic1)
-                || method.IsClosedFormOf(String_Join_generic2)))
+                || method.IsClosedFormOf(String_Join_generic2))
+            && arguments[1].TypeMapping is NpgsqlArrayTypeMapping)
         {
             // If the array of strings to be joined is a constant (NewArrayExpression), we translate to concat_ws.
             // Otherwise we translate to array_to_string, which also supports array columns and parameters.