Fixed a bug with postgresql and mysql migration folders as well as compilation warning related to it

src/NadekoBot/Migrations/Mysql/20220808141855_remove-obsolete-xp-columns.cs

@@ -0,0 +1,49 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace NadekoBot.Migrations.Mysql
+{
+    public partial class removeobsoletexpcolumns : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "lastlevelup",
+                table: "userxpstats");
+
+            migrationBuilder.DropColumn(
+                name: "lastlevelup",
+                table: "discorduser");
+
+            migrationBuilder.DropColumn(
+                name: "lastxpgain",
+                table: "discorduser");
+        }
+
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<DateTime>(
+                name: "lastlevelup",
+                table: "userxpstats",
+                type: "datetime(6)",
+                nullable: false,
+                defaultValueSql: "(UTC_TIMESTAMP)");
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "lastlevelup",
+                table: "discorduser",
+                type: "datetime(6)",
+                nullable: false,
+                defaultValueSql: "(UTC_TIMESTAMP)");
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "lastxpgain",
+                table: "discorduser",
+                type: "datetime(6)",
+                nullable: false,
+                defaultValueSql: "(UTC_TIMESTAMP - INTERVAL 1 year)");
+        }
+    }
+}