barretenberg: aarm64 binaries are mislabelled

[Maddiaa0]

Compiled binaries for aarm64 are actually x86_64 under the hood.

This is likely a mislabeling in the github actions and should be a small fix

repro:

install the mac amd64 bin

% nargo backend install acvm-backend-barretenberg-2 https://github.com/AztecProtocol/barretenberg/releases/download/barretenberg-v0.5.1/barretenberg-aarch64-apple-
darwin.tar.gz                 

# Go to dir
% cd ~/.nargo/backends                                                                                                                                                                           
% cd acvm-backend-barretenberg-2                                                                                                                                                 ~/.nargo/backends 

# describe the file
% file backend_binary                                                                                                                                ~/.nargo/backends/acvm-backend-barretenberg-2 mainframe
backend_binary: Mach-O 64-bit x86_64 executable, flags:<NOUNDEFS|DYLDLINK|TWOLEVEL|WEAK_DEFINES|BINDS_TO_WEAK|PIE>

[Savio-Sou]

Workaround:
The community has been compiling barretenberg from source for better performance on ARM-based Macs.

[Savio-Sou]

Noir users would have to wait for:

1. A new barretenberg version is released with the new aarm64 binary
2. A new Noir version that integrates and makes use of the new bb bin is released

to fully enjoy an aarm64 barretenberg proving experience.