Fix CI: install Node.js so actions/checkout can run in the container

The git fix alone got further, but actions/checkout@v4 (and later,
actions/upload-artifact@v4) are Node-based actions — Gitea Actions
execs their JS bundle with the "node" binary from inside the job's
own container rather than injecting a runtime of its own, and
vbatts/slackware:15.0 has no nodejs package anywhere on the official
Slackware mirror. Install a pinned, checksum-verified Node.js release
straight from nodejs.org in the same "Install git" step, matching the
existing Go/Rust bootstrap style in setup-slackware-buildenv.sh.
Verified end-to-end (node --version succeeds after a fresh install) in
vbatts/slackware:15.0 on the actual runner host.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.github/workflows/build-packages.yml

@@ -60,8 +60,19 @@ on:
 # resolve everything from the same prioritized repo set (patches over
 # main, see /etc/slackpkg/slackpkg.conf's PRIORITY) keeps every package on
 # this image on a mutually consistent version set.
+#
+# actions/checkout and actions/upload-artifact are both Node-based actions
+# — Gitea Actions execs their JS bundle with the "node" binary found
+# inside the job's own container, it does not inject a runtime of its
+# own. Slackware has no nodejs package at all (checked: not in any of the
+# main/extra/pasture/testing repos), so the "Install git" step also
+# installs a pinned, checksum-verified Node.js release directly from
+# nodejs.org — the same style already used for Go/Rust in
+# scripts/ci/setup-slackware-buildenv.sh.
 env:
   SLACKWARE_IMAGE: "vbatts/slackware:15.0"
+  NODE_VERSION: "20.20.2"
+  NODE_SHA256: "df770b2a6f130ed8627c9782c988fda9669fa23898329a61a871e32f965e007d"
 
 jobs:
   build:
@@ -72,7 +83,7 @@ jobs:
     outputs:
       artifact-name: ${{ steps.artifact-name.outputs.value }}
     steps:
-      - name: Install git (needed before actions/checkout can run)
+      - name: Install git and Node.js (needed before actions/checkout can run)
         run: |
           set -eu
           command -v tar > /dev/null || (echo "!! base image is missing tar — see SLACKWARE_IMAGE in this workflow" && exit 1)
@@ -102,6 +113,20 @@ jobs:
 
           git --version
 
+          # curl isn't installed until scripts/ci/setup-slackware-buildenv.sh
+          # runs, later — use wget (present in the base image) here instead.
+          # wget does not consult the system CA bundle on its own (unlike
+          # curl/git, which respect CURL_CA_BUNDLE/GIT_SSL_CAINFO), so pass
+          # it explicitly via --ca-certificate.
+          node_tarball="node-v${NODE_VERSION}-linux-x64.tar.xz"
+          wget -q --tries=3 --ca-certificate=/etc/ssl/certs/ca-certificates.crt \
+            -O "/tmp/$node_tarball" "https://nodejs.org/dist/v${NODE_VERSION}/$node_tarball"
+          echo "${NODE_SHA256}  /tmp/$node_tarball" | sha256sum -c -
+          mkdir -p /usr/local/lib/nodejs
+          tar -xf "/tmp/$node_tarball" -C /usr/local/lib/nodejs
+          echo "/usr/local/lib/nodejs/node-v${NODE_VERSION}-linux-x64/bin" >> "$GITHUB_PATH"
+          "/usr/local/lib/nodejs/node-v${NODE_VERSION}-linux-x64/bin/node" --version
+
       - uses: actions/checkout@v4
 
       - name: Set up Slackware build environment