Fix flaky ViewTest which would fail encoding null value

[scwhittle]

If there were no elements between early trigger and on-time global window firing due to previous on time behavior of firing when non-empty a null latest value would be output and be unencodable.

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[gemini-code-assist]

Summary of Changes

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This pull request resolves a flakiness issue in a specific test case within the Apache Beam SDK. The test, ViewTest.java, was prone to failure when a Latest.combineFn() operation produced a null value that could not be encoded. The fix ensures the test's reliability by adjusting the windowing strategy to prevent the emission of such null values under certain conditions.

Highlights

• Test Stability: Fixed a flaky ViewTest that would intermittently fail due to an unencodable null value being produced by the Latest.combineFn() in specific windowing scenarios.
• Windowing Behavior: Modified the window configuration within the testTriggeredLatestSingleton test case to explicitly set the onTimeBehavior to FIRE_IF_NON_EMPTY, preventing the output of null values when no elements are present.

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R: @chamikaramj for label java.

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