ci: improve caches #1813

Job	Run time
Check docs	34s
Check	1m 11s
Build	2m 3s
Clippy	1m 47s
Format	21s
Run Hermit for Rust (x86_64 + kvm)	3m 58s
Run (x86_64, rusty_demo, none, dev)	4m 48s
Test	1m 52s
Run (x86_64, rusty_demo, none, release)	3m 56s
Run (x86_64, httpd, virtio-net-pci, dev)	3m 20s
Run (x86_64, httpd, virtio-net-pci, release)	3m 23s
Run (x86_64, httpd, rtl8139, dev)	2m 56s
Run (x86_64, httpd, rtl8139, release)	3m 20s
Run (x86_64, testudp, virtio-net-pci, dev)	4m 23s
Run (x86_64, testudp, virtio-net-pci, release)	3m 5s
Run (x86_64, testudp, rtl8139, dev)	2m 55s
Run (x86_64, testudp, rtl8139, release)	3m 38s
Run (x86_64, hello_world, none, dev)	2m 32s
Run (x86_64, hello_world, none, release)	2m 45s
Run (aarch64, rusty_demo, none, dev)	4m 10s
Run (aarch64, rusty_demo, none, release)	3m 12s
Run (aarch64, httpd, virtio-net-pci, dev)	4m 23s
Run (aarch64, httpd, virtio-net-pci, release)	3m 29s
Run (aarch64, testudp, virtio-net-pci, dev)	3m 9s
Run (aarch64, testudp, virtio-net-pci, release)	4m 43s
	1h 15m 53s

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