client: allow non-octal chmod config for fileop.copy #5007

Job	Run time
govulncheck	56s
prepare	7s
binaries (darwin/amd64)	1m 10s
binaries (darwin/arm64)	56s
binaries (linux/amd64)	2m 4s
binaries (linux/arm/v7)	2m 2s
binaries (linux/arm64)	2m 9s
binaries (linux/s390x)	2m 0s
binaries (linux/ppc64le)	1m 56s
binaries (linux/riscv64)	1m 57s
binaries (windows/amd64)	1m 48s
binaries (windows/arm64)	1m 31s
test / prepare	2m 2s
test / run (containerd, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	7m 40s
test / run (containerd-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integr...	8m 54s
test / run (containerd-1.6, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	7m 55s
test / run (containerd-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./fronte...	8m 26s
test / run (oci, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	5m 11s
test / run (oci-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	5m 31s
test / run (oci-rootless-slirp4netns-detachnetns, ./client ./cmd/buildctl ./worker/containerd ./solver ....	5m 12s
test / run (oci-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, int...	5m 41s
test / run (./..., 1, integration gateway)	4m 31s
test / run (./client, containerd, nydus, integration)	7m 53s
test / run (./client, oci, nydus, integration)	4m 47s
test / run (./..., nydus, 1, integration)	4m 42s
image	8m 53s
image (rootless)	8m 46s
release	7s
scout	0s
	1h 54m 47s

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