tools/syz-covermerger: upload coverage as jsonl #14860

Job	Run time
build	3m 30s
aux	4m 54s
dashboard	3m 58s
arch (presubmit_arch_linux)	11m 25s
gvisor	4m 14s
old	6m 37s
arch (presubmit_arch_freebsd)	6m 34s
race	7m 54s
arch (presubmit_arch_netbsd)	4m 27s
race_dashboard	4m 43s
arch (presubmit_arch_openbsd)	4m 22s
arch (presubmit_arch_darwin)	4m 22s
arch (presubmit_arch_windows)	3m 31s
arch (presubmit_arch_executor)	3m 15s
	1h 13m 46s

Provide feedback