test(plugins): allow time for Windows legacy migration workflows (#8112)

The migration case runs real Git operations and several plugin subprocess restarts. Windows CI exceeded its 30-second test deadline and entered cleanup while the operation was still active. Keep every assertion and allow 60 seconds for the complete workflow.

packages/server/src/server/plugins/index.posix.test.ts

@@ -730,7 +730,7 @@ export default function contribute(server: PluginServerContext) {
         await service.stopAllPlugins();
       }
     },
-    30_000,
+    60_000,
   );
 
   it("keeps the running commit when a Git update build command fails", async () => {