Do not include a cache mount's ID in the ExecOp's cachemap #2549

Job	Run time
prepare	6s
binaries (darwin/amd64)	1m 17s
binaries (darwin/arm64)	2m 52s
binaries (linux/amd64)	2m 24s
binaries (linux/arm/v7)	3m 4s
binaries (linux/arm64)	3m 13s
binaries (linux/s390x)	3m 29s
binaries (linux/ppc64le)	2m 14s
binaries (linux/riscv64)	2m 20s
binaries (windows/amd64)	1m 19s
binaries (windows/arm64)	1m 5s
test / prepare	1m 55s
test / run (containerd, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	42m 41s
test / run (containerd-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integr...	8m 55s
test / run (containerd-1.6, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	7m 13s
test / run (containerd-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./fronte...	8m 8s
test / run (oci, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	4m 54s
test / run (oci-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	4m 52s
test / run (oci-rootless-slirp4netns-detachnetns, ./client ./cmd/buildctl ./worker/containerd ./solver ....	6m 2s
test / run (oci-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, int...	5m 32s
test / run (./..., 1, integration gateway)	4m 10s
test / run (./client, containerd, nydus, integration)	7m 7s
test / run (./client, oci, nydus, integration)	5m 21s
test / run (./..., nydus, 1, integration)	4m 0s
image	0s
release	0s
	2h 14m 13s

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