Miri: disable macOS testing for now

Author: RalfJung

Diff for: src/ci/docker/host-x86_64/x86_64-gnu-tools/checktools.sh

@@ -28,4 +28,5 @@ python3 "$X_PY" test --stage 2 src/tools/miri
 # We natively run this script on x86_64-unknown-linux-gnu and x86_64-pc-windows-msvc.
 # Also cover some other targets (on both of these hosts) via cross-testing.
 python3 "$X_PY" test --stage 2 src/tools/miri --target i686-pc-windows-msvc
-python3 "$X_PY" test --stage 2 src/tools/miri --target aarch64-apple-darwin
+#FIXME(https://github.com/rust-lang/rust/issues/103519): macOS testing is currently disabled
+# python3 "$X_PY" test --stage 2 src/tools/miri --target aarch64-apple-darwin