ci(linux32): make Javascript Actions work in x86 mode

In February 2023, older `actions/upload-artifact` were deprecated:
https://github.blog/changelog/2024-02-13-deprecation-notice-v1-and-v2-of-the-artifact-actions/
This was recently followed by brown-outs.

However, the `linux32` job relied on those, as there are well-documented
problems (see actions/runner#2115 for example)
running modern, Javascript-based Actions in 32-bit only containers.

To get the CI builds to work again, a work-around was implemented in
https://lore.kernel.org/git/20240912094841.GD589828@coredump.intra.peff.net
to let the 32-bit container make use of the 64-bit node 20 provided by
the Actions runner.

This, however, runs the risk of using 64-bit executables when we
purposefully chose a Docker image that only contains 32-bit bits and
pieces so that accidental use of 64-bit libraries or executables would
not happen.

Let's go about this the other way round instead, by overriding the amd64
version of node 20 the Actions runner provides with an x86 one (which is
"officially unofficial" by virtue of being hosted on
unofficial-builds.nodejs.org).

This allows us to stop using the now-deprecated versions of
`actions/checkout` and `actions/upload-artifact` before these Actions
became Javascript-based Actions.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

.github/workflows/main.yml

@@ -348,19 +348,27 @@ jobs:
       jobname: ${{matrix.vector.jobname}}
       distro: ${{matrix.vector.distro}}
     runs-on: ubuntu-latest
-    container: ${{matrix.vector.image}}
+    container:
+      image: ${{matrix.vector.image}}
+      volumes:
+        # override /__e/node20 on 32-bit because it is 64-bit
+        - /tmp:/__e${{matrix.vector.jobname != 'linux32' && '-x86' || ''}}/node20
     steps:
-    - uses: actions/checkout@v4
-      if: matrix.vector.jobname != 'linux32'
-    - uses: actions/checkout@v1 # cannot be upgraded because Node.js Actions aren't supported in this container
+    - name: prepare x86 variant of node20
       if: matrix.vector.jobname == 'linux32'
+      run: |
+        apt -q update && apt -q -y install curl &&
+        NODE_URL=https://unofficial-builds.nodejs.org/download/release/v20.17.0/node-v20.17.0-linux-x86.tar.gz &&
+        curl -Lo /tmp/node.tar.gz $NODE_URL &&
+        tar -C /__e/node20 -x --strip-components=1 -f /tmp/node.tar.gz
+    - uses: actions/checkout@v4
     - run: ci/install-dependencies.sh
     - run: ci/run-build-and-tests.sh
     - name: print test failures
       if: failure() && env.FAILED_TEST_ARTIFACTS != ''
       run: ci/print-test-failures.sh
     - name: Upload failed tests' directories
-      if: failure() && env.FAILED_TEST_ARTIFACTS != '' && matrix.vector.jobname != 'linux32'
+      if: failure() && env.FAILED_TEST_ARTIFACTS != ''
       uses: actions/upload-artifact@v4
       with:
         name: failed-tests-${{matrix.vector.jobname}}