fix: util/path: `CheckSystemDriveAndRemoveDriveLetter` to preserve `/` #4809

Job	Run time
govulncheck	1m 2s
prepare	4s
binaries (darwin/amd64)	1m 10s
binaries (darwin/arm64)	58s
binaries (linux/amd64)	2m 7s
binaries (linux/arm/v7)	1m 56s
binaries (linux/arm64)	2m 5s
binaries (linux/s390x)	1m 58s
binaries (linux/ppc64le)	1m 57s
binaries (linux/riscv64)	2m 8s
binaries (windows/amd64)	1m 49s
binaries (windows/arm64)	1m 35s
test / prepare	1m 45s
test / run (containerd, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	3m 30s
test / run (containerd-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integr...	3m 32s
test / run (containerd-1.6, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	3m 25s
test / run (containerd-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./fronte...	3m 24s
test / run (oci, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	3m 32s
test / run (oci-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	3m 21s
test / run (oci-rootless-slirp4netns-detachnetns, ./client ./cmd/buildctl ./worker/containerd ./solver ....	3m 26s
test / run (oci-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, int...	3m 26s
test / run (./..., 1, integration gateway)	3m 28s
test / run (./client, containerd, nydus, integration)	3m 22s
test / run (./client, oci, nydus, integration)	3m 21s
test / run (./..., nydus, 1, integration)	3m 22s
image	1s
release	1s
scout	1s
	1h 1m 46s

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