[Snek] [keith-packard/snek] c54a50: .github: Use debian versions of qemu

[Keith Packard]

  Branch: refs/heads/str-builtin
  Home:   https://github.com/keith-packard/snek
  Commit: c54a506f54e1724f6f9b8ec39d8d8cb336af14a6
      https://github.com/keith-packard/snek/commit/c54a506f54e1724f6f9b8ec39d8d8cb336af14a6
  Author: Keith Packard <keithp at keithp.com>
  Date:   2021-12-12 (Sun, 12 Dec 2021)

  Changed paths:
    M .github/Dockerfile

  Log Message:
  -----------
  .github: Use debian versions of qemu

Don't need custom version of qemu for risc-v any more.

Signed-off-by: Keith Packard <keithp at keithp.com>