Run experiment 3

This varies:

- `ubuntu-22.04-arm` vs. `ubuntu-24.04.arm` GHA runner.
- Installing Rust via the `rust-toolchain` action vs. with curl.sh.
- Installing the stable vs. beta Rust toolchain.
- Installing nextest via `install-action` quickinstall/binstall.

*If* this also confirms that the only fully consistent factor in
whether errors happen is `ubuntu-22.04-arm` vs. `ubuntu-24.04.arm`,
then that will make it clearer that the problem is likely specific
to the `ubuntu-24.04.arm` runner.

See #1790 and rust-lang/rust#135867 for context.

Author: EliahKagan

.github/workflows/arm-segv-experiment.yml

@@ -6,12 +6,12 @@ jobs:
   test-fast:
     strategy:
       matrix:
-        num-high: [ 0 ]  # [ 0, 1, 2 ]
+        num-high: [ 0, 1, 2, 3 ]
         os-ver: [ '22.04', '24.04' ]
-        channel: [ stable, beta, nightly ]
+        channel: [ stable, beta ]  # `gix-macros::macros momo::ux` currently fails on `nightly`.
         get-rust-by: [ rt-action, curl-sh ]
         get-nextest-by: [ i-action, cargo-qi ]
-        num-low: [ 0 ]  # [ 0, 1, 2 ]
+        num-low: [ 0, 1, 2, 3 ]
 
       fail-fast: false