github: instruct dependabot to also look after the stable-5.0 branch #6637

Job	Run time
Code	8m 29s
Client (1.20.x, ubuntu-latest)	1m 22s
System (1.20.x, cluster, dir)	12m 54s
Client (1.20.x, macos-latest)	1m 28s
Documentation	10m 4s
System (1.20.x, cluster, btrfs)	13m 58s
Client (1.20.x, windows-latest)	2m 16s
System (1.20.x, cluster, lvm)	13m 38s
System (1.20.x, cluster, zfs)	13m 49s
System (1.20.x, cluster, ceph)	18m 17s
System (1.20.x, cluster, random)	13m 38s
System (1.20.x, standalone, dir)	22m 25s
System (1.20.x, standalone, btrfs)	22m 9s
System (1.20.x, standalone, lvm)	39m 49s
System (1.20.x, standalone, zfs)	44m 1s
System (1.20.x, standalone, ceph)	1h 12m 55s
System (1.20.x, standalone, random)	30m 55s
System (stable, cluster, dir)	12m 24s
System (stable, standalone, dir)	22m 25s
System (tip, cluster, dir)	12m 42s
System (tip, standalone, dir)	22m 37s
Trigger snap edge build	0s
	6h 52m 15s

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