dockerfile: pin dockerfile frontend image #4971

Job	Run time
govulncheck	58s
prepare	11s
binaries (darwin/amd64)	1m 10s
binaries (darwin/arm64)	1m 0s
binaries (linux/amd64)	2m 7s
binaries (linux/arm/v7)	2m 13s
binaries (linux/arm64)	2m 8s
binaries (linux/s390x)	1m 54s
binaries (linux/ppc64le)	2m 18s
binaries (linux/riscv64)	2m 15s
binaries (windows/amd64)	1m 34s
binaries (windows/arm64)	1m 36s
test / prepare	1m 48s
test / run (containerd, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	7m 52s
test / run (containerd-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integr...	9m 14s
test / run (containerd-1.6, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	7m 26s
test / run (containerd-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./fronte...	8m 31s
test / run (oci, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	5m 17s
test / run (oci-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	5m 23s
test / run (oci-rootless-slirp4netns-detachnetns, ./client ./cmd/buildctl ./worker/containerd ./solver ....	5m 21s
test / run (oci-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, int...	5m 3s
test / run (./..., 1, integration gateway)	4m 0s
test / run (./client, containerd, nydus, integration)	7m 35s
test / run (./client, oci, nydus, integration)	4m 54s
test / run (./..., nydus, 1, integration)	4m 14s
image	8m 46s
image (rootless)	8m 41s
release	6s
scout	0s
	1h 53m 35s

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