Rev DevTools to 2.1.1 for tests (flutter#81515)

Author: goderbauer

dev/devicelab/lib/tasks/perf_tests.dart

@@ -1445,7 +1445,7 @@ class DevToolsMemoryTest {
       'global',
       'activate',
       'devtools',
-      '2.0.0',
+      '2.1.1',
     ]);
     _devToolsProcess = await startProcess(
       pubBin,