[CQ] fix unchecked assignment (#8368)

Follow-up from #8367, a
missed unchecked assignment.

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Author: pq

src/io/flutter/test/DartTestEventsConverterZ.java

@@ -101,7 +101,7 @@ public DartTestEventsConverterZ(@NotNull final String testFrameworkName,
                                   @NotNull final DartUrlResolver urlResolver) {
     super(testFrameworkName, consoleProperties);
     myUrlResolver = urlResolver;
-    myTestIdToTimestamp = new HashMap();
+    myTestIdToTimestamp = new HashMap<>();
     myTestData = new HashMap<>();
     myGroupData = new HashMap<>();
     mySuiteData = new HashMap<>();