Fix final CS1061 and CS0103 errors: add missing System.Linq and System.Text.RegularExpressions using directives

Co-authored-by: renemadsen <76994+renemadsen@users.noreply.github.com>

Author: Copilot

test/EFCore.MySql.FunctionalTests/Query/NonSharedPrimitiveCollectionsQueryMySqlTest.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Infrastructure;

test/EFCore.MySql.FunctionalTests/Query/NorthwindFunctionsQueryMySqlTest.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Linq;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using Microsoft.EntityFrameworkCore.Query;
 using Microsoft.EntityFrameworkCore.TestModels.Northwind;