perf(nix-eval): reduce worker count to prevent OOM

Author: yvan-sraka

nix/packages/github-matrix/github_matrix.py

@@ -311,7 +311,7 @@ def main() -> None:
 
     args = parser.parse_args()
 
-    max_workers: int = os.cpu_count() or 1
+    max_workers: int = int(os.cpu_count() / 2) or 1
 
     cmd = build_nix_eval_command(max_workers, args.flake_outputs)