Bump version for v1.15.38 release #246

Job	Run time
Run test and build (macos-15-intel)	4m 33s
Run test and build (ubuntu-24.04-arm)	45s
Run test and build (ubuntu-latest)	54s
Run test and build (macos-14)	1m 14s
Run test and build (macos-15)	1m 34s
	9m 0s

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