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    2 089 suites   - 525   54m 24s ⏱️ - 24m 36s
  6 412 tests ±       0    5 891 ✔️ ±       0  521 💤 ±  0  0 ❌ ±0 
35 681 runs   - 8 935  35 027 ✔️  - 8 871  654 💤  - 64  0 ❌ ±0 

Results for commit 59e7b03. ± Comparison against base commit f61a1e1.

♻️ 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.