qemu: use 9p by default #5023

Job	Run time
Lints	2m 31s
Windows tests	4m 45s
Integration tests	10m 37s
Integration tests (on Linux) (alpine.yaml)	5m 6s
Unit tests (1.21.x)	45s
Integration tests (on Linux) (debian.yaml)	7m 56s
Unit tests (1.22.x)	3m 34s
Integration tests (on Linux) (fedora.yaml)	7m 8s
Integration tests (on Linux) (archlinux.yaml)	8m 10s
Integration tests (on Linux) (opensuse.yaml)	6m 48s
Colima (v0.6.5)	6m 20s
Integration tests (on Linux) (experimental/net-user-v2.yaml)	6m 30s
Integration tests (on Linux) (experimental/9p.yaml)	6m 49s
Upgrade test (v0.15.1)	8m 27s
Integration tests (on Linux) (docker.yaml)	7m 45s
Integration tests (on Linux) (../hack/test-templates/alpine-9p-writable.yaml)	4m 24s
Integration tests (on Linux) (../hack/test-templates/test-misc.yaml)	18m 48s
VMNet test	23m 36s
vz (experimental/vz.yaml)	11m 38s
vz (fedora.yaml)	10m 12s
	2h 41m 49s

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