Pin docker platform and fix build

Avoid surprises when building images in MacOS

root@61f5bb9296d6:/# redoxer check
rosetta error: failed to open elf at /lib64/ld-linux-x86-64.so.2
 redoxer cargo: signal: 5 (SIGTRAP) (core dumped)

Also fix docker build (accidentally deletes .cargo/bin)