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

src/NadekoBot/Migrations/PostgreSql/20220727033944_linkonly-channels.cs

@@ -0,0 +1,26 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace NadekoBot.Migrations.PostgreSql
+{
+    public partial class linkonlychannels : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<int>(
+                name: "type",
+                table: "imageonlychannels",
+                type: "integer",
+                nullable: false,
+                defaultValue: 0);
+        }
+
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "type",
+                table: "imageonlychannels");
+        }
+    }
+}