Redo experiment 1 with current beta and nightly

When using `dtolnay/rust-toolchain` with the `toolchain` key to
specify a channel, the action version should be given as `@master`.
But I accidentally kept it at `@stable`! This caused `beta` and
`nightly` to refer to the most recent beta and nightly builds
*prior* to the current stable version. That made the conclucions
about beta and nightly builds inaccurate. This rectifies that
error and repeats the experiment.

See e71b0cf (1f3f6b5), #1790, and rust-lang/rust#135867 for context.

(I made this mistake in both experiment 1 and experiment 2, having
wrongly thought I'd changed `@stable` to `@master` for experiment
1. This commit just repeats experiment 1, but experiment 2 should
also be repeated for the same reason.)

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

@@ -6,27 +6,27 @@ jobs:
   test-fast:
     strategy:
       matrix:
-        num-high: [ 0, 1, 2, 3, 4, 5, 6, 7 ]
         os-ver: [ '22.04', '24.04' ]
         channel: [ stable, beta ]  # `gix-macros::macros momo::ux` currently fails on `nightly`.
-        num-low: [ 0, 1, 2, 3, 4, 5, 6, 7 ]
+        increase-stack: [ false, true ]
+        number: [ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' ]
 
       fail-fast: false
 
     runs-on: ubuntu-${{ matrix.os-ver }}-arm
 
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.channel }}
       # - uses: Swatinem/rust-cache@v2
       - uses: taiki-e/install-action@v2
         with:
           tool: nextest
-      # - name: Set RUST_MIN_STACK
-      #   if: matrix.increase-stack
-      #   run: echo RUST_MIN_STACK=16777216 >>"$GITHUB_ENV"
+      - name: Set RUST_MIN_STACK
+        if: matrix.increase-stack
+        run: echo RUST_MIN_STACK=16777216 >>"$GITHUB_ENV"
       - name: Test (nextest)
         env:
           GIX_TEST_CREATE_ARCHIVES_EVEN_ON_CI: '1'