Draft experiment 3 to try more ways to install

In case the installation method makes a difference.

Also, this brings back testing of the unstable toolchain.

This has just one job for each meaningful combination, so mistakes
in the experiment workflow can be found before doing nine times
as much work. The experiment this prepares should hopefully shed
more light on GitoxideLabs#1790 (or increase confidence in the observations so
far), but this is just preparation: variation across runs will
likely be due to the bug being nondeterministic.

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

@@ -6,27 +6,40 @@ jobs:
   test-fast:
     strategy:
       matrix:
-        num-high: [ 0, 1, 2, 3, 4, 5, 6, 7 ]
+        num-high: [ 0 ]  # [ 0, 1, 2 ]
         os-ver: [ '22.04', '24.04' ]
-        channel: [ stable, beta ]
-        num-low: [ 0, 1, 2, 3, 4, 5, 6, 7 ]
+        channel: [ stable, beta, nightly ]
+        get-rust-by: [ rt-action, curl-sh ]
+        get-nextest-by: [ i-action, cargo-qi ]
+        num-low: [ 0 ]  # [ 0, 1, 2 ]
 
       fail-fast: false
 
     runs-on: ubuntu-${{ matrix.os-ver }}-arm
 
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@master
+      - if: matrix.get-rust-by == 'rt-action'
+        uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.channel }}
+      - if: matrix.get-rust-by == 'curl-sh'
+        name: Install Rust via sh.rustup.rs
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs |
+            sh -s -- -y --default-toolchain ${{ matrix.channel }}
+          echo "PATH=$HOME/.cargo/bin:$PATH" >> "$GITHUB_ENV"
       # - uses: Swatinem/rust-cache@v2
-      - uses: taiki-e/install-action@v2
+      - if: matrix.get-nextest-by == 'i-action'
+        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"
+      - if: matrix.get-nextest-by == 'cargo-qi'
+        name: Install nextest with quickinstall/binstall
+        run: |
+          cargo install cargo-quickinstall
+          cargo quickinstall cargo-binstall
+          cargo quickinstall cargo-nextest
       - name: Test (nextest)
         env:
           GIX_TEST_CREATE_ARCHIVES_EVEN_ON_CI: '1'