selftest/reproducible: Exclude rust/rust-dbg for now until we can fix

selftest/reproducible: Exclude rust/rust-dbg for now until we can fix

There looks to be a reproducibility issue left in one of the rust
libraries. It doesn't appear to be a string issue but some binary
problem. Disable rust from the reproducibility testing until we can
get to the bottom of the issue (allowing wider testing of all the
other improvements).

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>