Fix flakey tests

[xiedaxia1hao]

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This PR fixes 2 potential flaky tests in MapKeyValueAdapterUnitTests.java file.

In the test scanShouldIterateOverAvailableEntries(), we rely on the fact that the map has a specific order. However, as the key space map for COLLECTION_1 is initialized as a ConcurrentHashMap, it is not guaranteed that the order will remain constant over time according to the Java documentation.

Because the elements of a ConcurrentHashMap are not ordered in any particular way, and may be processed in different orders in different parallel executions, the correctness of supplied functions should not depend on any ordering, or on any other objects or values that may transiently change while computation is in progress;

Such indeterministic characteristic of ConcurrentHashMap will cause this test to fail in some platforms or specific machines that adopt a different iteration order.

To fix it, I will first iterate through all the entries in the map, and based on the key of the first entry, we then compare two entries accordingly.

The same fix also applies to scanDoesNotMixResultsFromMultipleKeyspaces().