Bump crossbeam-channel from 0.5.13 to 0.5.15 in /gc/mmtk in the cargo group across 1 directory #643

Job	Run time
make (check, --disable-yjit)	6m 40s
make (check, cppflags=-DVM_CHECK_MODE)	8m 12s
make (check, --enable-shared --enable-load-relative)	6m 58s
make (test-bundler-parallel, 50)	32m 19s
make (check, i686)	10m 8s
make (check, ubuntu-24.04-arm)	7m 42s
make (check, ubuntu-24.04)	8m 1s
make (test-bundled-gems)	17m 34s
Ubuntu result	4s
	1h 37m 38s

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