Make experimental_shell_command deterministic (#16675)
Make experimental_shell_command deterministic (#16675)

`set` bad, `tuple` good.
benjyw/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants