Revert "Try running on node-20 image"

This reverts commit 7037d24602668d1f5fcc29bd5b9aa5f90458c4ef.

.gitea/workflows/publish.yaml

@@ -4,13 +4,19 @@ on: [push]
 
 jobs:
   Explore-Gitea-Actions:
-    # Interesting discussion [here](https://gitea.com/gitea/act_runner/issues/538)
-    runs-on: node-20
+    runs-on: ubuntu-latest
     steps:
       - run: echo "🎉 The job was automatically triggered by a ${{ gitea.event_name }} event."
       - run: echo "🐧 This job is now running on a ${{ runner.os }} server hosted by Gitea!"
       - run: echo "🔎 The name of your branch is ${{ gitea.ref }} and your repository is ${{ gitea.repository }}."
 
+      # Despite not being present in the QuickStart instructions, this step is necessary in order to install `node`,
+      # which is itself required for `actions/checkout`
+      # Cannot use `actions/setup-node` because that _itself_ requires `node` (it makes it available to user-code,
+      # rather than to the system. Interesting discussion [here](https://gitea.com/gitea/act_runner/issues/538))
+      - name: Install node
+        run: apt-get install -y node
+
       - name: Check out repository code
         uses: actions/checkout@v4