fix(actions): update actions/cache action to v4(#79)

.github/workflows/ubuntu18-v9.0.0-build.yaml

@@ -1,6 +1,9 @@
 name: ubuntu18.04 v9.0.0 build x86-64
 run-name: ubuntu18 x86-64
 
+# make GHA actions use node16 which still works with bionic
+# See https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/
+# Unclear how long this will work though
 env:
   ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true
 
@@ -20,9 +23,17 @@ jobs:
       image: docker://ubuntu:18.04
       options: --volume ${{ github.workspace }}:/workspace/${{ github.repository }}
     steps:
+      - name: Setup environment
+        # Ubuntu 18.04 has a GLib version too old for nodejs20 or later,
+        # so, in order to do the tests, we must allow to use an older version.
+        # https://github.com/actions/checkout/issues/1590
+        # In that thread, Flamefire proposed this same solution:
+        # https://github.com/boostorg/nowide/commit/d4aa719f21149de8960247403435e9b794a01255
+        run: |
+          echo "GHA_USE_NODE_20=false" >> $GITHUB_ENV
+          echo "ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true" >> $GITHUB_ENV
       - name: Check out repository code
-        uses: actions/checkout@v3
-
+        uses: actions/checkout@v4
       - name: Install
         env:
           DEBIAN_FRONTEND: noninteractive