Signed-off-by: Ron Shavit <me@ronshavit.com>

This is needed to support VS Code with clangd for userspace keymaps (in
this case `compile_commands.json` and `.cache/clangd` are located in the
`qmk_userspace` working copy).

- folder name inside dev container is same as folder name on host
so if it differs from qmk_userspace then setup.sh cannot be found
and it sets incorrect user.overlay_dir
- docs https://containers.dev/implementors/json_reference/