tools/syz-covermerger: upload coverage as jsonl #14873

Job	Run time
aux	4m 54s
arch (presubmit_arch_linux)	10m 43s
build	10m 52s
arch (presubmit_arch_freebsd)	6m 33s
dashboard	3m 25s
old	6m 42s
arch (presubmit_arch_netbsd)	4m 27s
race	8m 47s
arch (presubmit_arch_openbsd)	4m 21s
race_dashboard	4m 44s
arch (presubmit_arch_darwin)	4m 26s
gvisor	4m 21s
arch (presubmit_arch_windows)	3m 21s
arch (presubmit_arch_executor)	3m 20s
	1h 20m 56s

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