[Backport next] github: downgrade upload-artifact to v3 #419

Job	Run time
generate_target_matrix	5s
build_firmware (ath79-generic)	1h 27m 16s
build_firmware (ath79-mikrotik)	1h 17m 13s
build_firmware (ath79-nand)	1h 18m 35s
build_firmware (bcm27xx-bcm2708)	1h 9m 33s
build_firmware (bcm27xx-bcm2709)	1h 17m 17s
build_firmware (bcm27xx-bcm2710)	1h 23m 36s
build_firmware (bcm27xx-bcm2711)	1h 26m 38s
build_firmware (ipq40xx-generic)	1h 20m 47s
build_firmware (ipq40xx-mikrotik)	1h 19m 41s
build_firmware (ipq806x-generic)	1h 19m 8s
build_firmware (lantiq-xrx200)	1h 20m 6s
build_firmware (lantiq-xway)	1h 35m 9s
build_firmware (mediatek-filogic)	1h 24m 1s
build_firmware (mediatek-mt7622)	1h 21m 55s
build_firmware (mpc85xx-p1010)	1h 17m 14s
build_firmware (mpc85xx-p1020)	1h 15m 20s
build_firmware (mvebu-cortexa9)	1h 14m 18s
build_firmware (ramips-mt7620)	1h 15m 48s
build_firmware (ramips-mt7621)	1h 19m 45s
build_firmware (ramips-mt76x8)	1h 19m 27s
build_firmware (realtek-rtl838x)	1h 4m 45s
build_firmware (rockchip-armv8)	1h 23m 11s
build_firmware (sunxi-cortexa7)	1h 11m 52s
build_firmware (x86-64)	1h 31m 10s
build_firmware (x86-generic)	1h 25m 24s
build_firmware (x86-geode)	1h 21m 52s
build_firmware (x86-legacy)	1h 22m 42s
create_release	0s
	1d 12h 3m 48s

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