release.nix: Use arm64-apple-darwin in bootstrapConfigs, not aarch64

Fix this config name for consistency with non-bootstrap platform config.
This also fixes a build failure of the bootstrap tools on
aarch64-darwin, where a test in LLVM 21 assumes it's spelt arm64, not
aarch64.

Also saves on having to rebuild LLVM just for bootstrap tools, now that
the config is consistent.

pkgs/stdenv/darwin/bootstrap-files/aarch64-apple-darwin.nix

@@ -1,3 +1,5 @@
+# FIXME: Changed to arm64-apple-darwin in release.nix stdenvBootstrapTools, please handle when refreshing
+
 # Autogenerated by maintainers/scripts/bootstrap-files/refresh-tarballs.bash as:
 # $ ./refresh-tarballs.bash --targets=aarch64-apple-darwin
 #

pkgs/top-level/release.nix

@@ -22,7 +22,7 @@
   supportedSystems ? builtins.fromJSON (builtins.readFile ../../ci/supportedSystems.json),
   # The platform triples for which we build bootstrap tools.
   bootstrapConfigs ? [
-    "aarch64-apple-darwin"
+    "arm64-apple-darwin"
     "aarch64-unknown-linux-gnu"
     "aarch64-unknown-linux-musl"
     "i686-unknown-linux-gnu"