Fix GcsEndpoint serialization in GcsOptions #40453

Job	Run time
Java Wordcount Direct Runner (self-hosted, ubuntu-20.04, main)	13m 35s
Java Unit Tests (windows-latest)	19m 1s
Java Wordcount Direct Runner (windows-latest)	24m 38s
Java Wordcount Direct Runner (macos-latest)	17m 21s
Java Unit Tests (self-hosted, ubuntu-20.04, main)	21m 33s
Java Unit Tests (macos-latest)	11m 8s
	1h 47m 16s

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