Eliminate uses of fuzzy arrows in pkg/testing (fix bots).

pkg/testing/lib/src/expectation.dart

Index: pkg/testing/lib/src/expectation.dart
diff --git a/pkg/testing/lib/src/expectation.dart b/pkg/testing/lib/src/expectation.dart
index 11ef0ee26b8c4286962b9f8c2f6deda4870770f1..3ba1af80f8787a51886235ad0ed6c2c6b38c854e 100644
--- a/pkg/testing/lib/src/expectation.dart
+++ b/pkg/testing/lib/src/expectation.dart
@@ -89,7 +89,9 @@ class ExpectationSet {
     for (Map map in data) {
       String name;
       String group;
-      map.forEach((String key, String value) {
+      map.forEach((_key, _value) {
+        String key = _key;
+        String value = _value;
         switch (key) {
           case "name":
             name = value;