dockerfile: mask usage of secret env in command name #4785

Job	Run time
build (windows/amd64)	1m 47s
build (windows/amd64)	1m 47s
build (freebsd/amd64)	1m 33s
build (freebsd/amd64)	1m 33s
test-freebsd-amd64	17m 17s
test-freebsd-amd64	17m 17s
test-windows-amd64 (containerd, ./client)	4m 47s
test-windows-amd64 (containerd, ./client)	4m 47s
test-windows-amd64 (containerd, ./cmd/buildctl)	4m 21s
test-windows-amd64 (containerd, ./cmd/buildctl)	4m 21s
test-windows-amd64 (containerd, ./worker/containerd)	4m 3s
test-windows-amd64 (containerd, ./worker/containerd)	4m 3s
test-windows-amd64 (containerd, ./solver)	2m 24s
test-windows-amd64 (containerd, ./solver)	2m 24s
test-windows-amd64 (containerd, ./frontend)	2m 24s
test-windows-amd64 (containerd, ./frontend)	2m 24s
test-windows-amd64 (containerd, ./frontend/dockerfile)	25m 37s
test-windows-amd64 (containerd, ./frontend/dockerfile)	25m 24s
test-windows-amd64 (./..., 1)	13m 42s
test-windows-amd64 (./..., 1)	13m 42s
	2h 35m 37s

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