correctly build arm64 macos Nim compiler

[narimiran]

Trying to see if the correct version of Nim compiler will be built on arm64 macos.

[github-actions]

Unit Test Results

       12 files   -        3    2 096 suites   - 524   57m 41s ⏱️ - 20m 13s
  6 362 tests ±       0    5 860 ✔️ ±       0  502 💤 ±  0  0 ❌ ±0 
35 384 runs   - 8 847  34 763 ✔️  - 8 790  621 💤  - 57  0 ❌ ±0 

Results for commit bfb99b0. ± Comparison against base commit 0769fc7.

♻️ This comment has been updated with latest results.

[etan-status]

As the arm64 test fails with a stacktrace and libunwind is used on macOS, maybe this helps:

• Bump nim-libbacktrace to 616e5f4a6e2c751b85487e2e855c6b7f90848503 #6919

[tersec]

As the arm64 test fails with a stacktrace and libunwind is used on macOS, maybe this helps:

* [Bump nim-libbacktrace to `616e5f4a6e2c751b85487e2e855c6b7f90848503` #6919](https://github.com/status-im/nimbus-eth2/pull/6919)

Merged into unstable.