Fix TypeError when --dest passed as string

[McVyp]

Running emu-docker create <emu> <img> --dest <path> throws:

TypeError: unsupported operand type(s) for /: 'str' and 'str'

args.dest comes in as a plain string from argparse (the --dest arg isn't typed as Path), but create_docker_image() tries to use / on it directly here:

https://github.com/google/android-emulator-container-scripts/blob/master/emu/emu_docker.py#L90

if not sys_docker.available() and not sys_docker.can_pull():
            sys_docker.build(args.dest / "sys_img")

Just wraps it in Path(), same as a few lines down for the emulator build:

emu_docker.build(Path(args.dest) / "emulator")

Tested on Ubuntu 26.04 LTS:

emu-docker create stable "C google_apis x86_64" --no-metrics --dest docker-src-37