feat(rootless): help detection with execv check "is current builder rootless?" #3940

Job	Run time
shellcheck	12s
fmt	6s
cargo-deny	21s
check	19s
clippy (macos-latest)	42s
generate-matrix	14s
clippy (ubuntu-latest)	20s
test (macos-latest)	2m 11s
clippy (windows-latest)	1m 5s
test (ubuntu-latest)	1m 19s
test (windows-latest)	3m 0s
remote	2m 16s
bisect	4m 50s
docker-in-docker	3m 48s
foreign	2m 37s
target (${{ matrix.pretty }},${{ matrix.os }})	0s
podman	0s
publish	0s
conclusion	1s
Coverage	6s
	23m 27s

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