make coverage work again (#29016)

diff --git a/dev/bots/test.dart b/dev/bots/test.dart
index bb41ead..509120c 100644
--- a/dev/bots/test.dart
+++ b/dev/bots/test.dart
@@ -572,7 +572,7 @@
   if (!shouldProcessOutput) {
     return runCommand(flutter, args,
       workingDirectory: workingDirectory,
-      expectNonZeroExit: true,
+      expectNonZeroExit: expectFailure,
       printOutput: printOutput,
       skip: skip,
       timeout: timeout,