gtk.cfg: Remove extra semicolons from g_return* macros (#8632) #20053

Job	Run time
build_cmake (ubuntu:25.10, true, true)	2m 44s
build_cmake (alpine:3.23, false, false)	4m 25s
build_make (alpine:3.23)	5m 43s
build_make (ubuntu:24.04)	2m 49s
build_make (ubuntu:25.10)	2m 55s
build_cmake (ubuntu:24.04, true, true)	2m 40s
	21m 16s

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