test: update hmr test to use flat routes, otherwise it'll fail due to…

… the warning ending up in stderr

Signed-off-by: Logan McAnsh <logan@mcan.sh>

integration/hmr-test.ts

@@ -14,6 +14,7 @@ let fixture = (options: { port: number; appServerPort: number }) => ({
       appServerPort: options.appServerPort,
     },
     unstable_tailwind: true,
+    v2_routeConvention: true,
   },
   files: {
     "package.json": `
@@ -124,7 +125,7 @@ let fixture = (options: { port: number; appServerPort: number }) => ({
           );
         }
       `,
-    "app/routes/index.tsx": `
+    "app/routes/_index.tsx": `
         import { useLoaderData } from "@remix-run/react";
         export default function Index() {
           const t = useLoaderData();