ci(linux32): do make Javascript Actions work

In 9c26185 (ci: use regular action versions for linux32 job,
2024-09-12), a hack was implemented 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
specifically chose a Docker image that only contains 32-bit bits and
pieces so that would not happen.

Let's address this instead by overriding the amd64 version of node 20
with an x86 one (which is "officially unofficial" by virtue of being
hosted on unofficial-builds.nodejs.org).

This partially reverts 9c26185 (ci: use regular action versions for
linux32 job, 2024-09-12), keeping the updates to Javascript Actions.

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

.github/workflows/main.yml

@@ -40,11 +40,19 @@ 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:
-    - name: prepare libc6 for actions
+    - name: prepare x86 variant of node20
       if: matrix.vector.jobname == 'linux32'
-      run: apt -q update && apt -q -y install libc6-amd64 lib64stdc++6
+      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