probe_executor fails inside a docker container

[Keno]

#37 413.7 ERROR: LoadError: IOError: realpath("/etc/resolv.conf/"): not a directory (ENOTDIR)
#37 413.7 Stacktrace:
#37 413.7   [1] uv_error
#37 413.7     @ ./libuv.jl:106 [inlined]
#37 413.7   [2] realpath(path::String)
#37 413.7     @ Base.Filesystem ./path.jl:506
#37 413.7   [3] (::Sandbox.var"#probe_overlay_mount#21"{Sandbox.var"#probe_overlay_mount#19#22"})(rootfs_path::String, mount_path::String; verbose::Bool, userxattr::Bool)
#37 413.7     @ Sandbox ~/.julia/packages/Sandbox/WhYeY/src/utils.jl:312
#37 413.7   [4] probe_overlay_mount
#37 413.7     @ ~/.julia/packages/Sandbox/WhYeY/src/utils.jl:302 [inlined]
#37 413.7   [5] find_persist_dir_root(rootfs_path::String, dir_hints::Vector{String}; verbose::Bool)
#37 413.7     @ Sandbox ~/.julia/packages/Sandbox/WhYeY/src/utils.jl:375
#37 413.7   [6] find_persist_dir_root (repeats 2 times)
#37 413.7     @ ~/.julia/packages/Sandbox/WhYeY/src/utils.jl:301 [inlined]
#37 413.7   [7] build_executor_command(exe::Sandbox.UnprivilegedUserNamespacesExecutor, config::Sandbox.SandboxConfig, user_cmd::Cmd)
#37 413.7     @ Sandbox ~/.julia/packages/Sandbox/WhYeY/src/UserNamespaces.jl:192
#37 413.7   [8] _run(run_or_success::typeof(run), exe::Sandbox.UnprivilegedUserNamespacesExecutor, config::Sandbox.SandboxConfig, user_cmd::Cmd)
#37 413.7     @ Sandbox ~/.julia/packages/Sandbox/WhYeY/src/Sandbox.jl:116
#37 413.7   [9] run
#37 413.7     @ ~/.julia/packages/Sandbox/WhYeY/src/Sandbox.jl:139 [inlined]
#37 413.7  [10] (::Sandbox.var"#95#96"{Bool, Sandbox.UnprivilegedUserNamespacesExecutor})(tmpdir::String)
#37 413.7     @ Sandbox ~/.julia/packages/Sandbox/WhYeY/src/Sandbox.jl:184
#37 413.7  [11] mktempdir(fn::Sandbox.var"#95#96"{Bool, Sandbox.UnprivilegedUserNamespacesExecutor}, parent::String; prefix::String)
#37 413.7     @ Base.Filesystem ./file.jl:819
#37 413.7  [12] mktempdir (repeats 2 times)
#37 413.7     @ ./file.jl:815 [inlined]
#37 413.7  [13] #probe_executor#94
#37 413.7     @ ~/.julia/packages/Sandbox/WhYeY/src/Sandbox.jl:156 [inlined]
#37 413.7  [14] probe_executor
#37 413.7     @ ~/.julia/packages/Sandbox/WhYeY/src/Sandbox.jl:155 [inlined]