Migrate to Node 20, clean up workflows (#2902)

Tests still appear to fail per #2898. Unfortunately, I need actions/runner#2347 to ignore the test failures properly - I need them to be warnings, not hard errors.

.github/workflows/test-next-push.yml

@@ -0,0 +1,30 @@
+name: test-next-push
+
+on:
+  push:
+    branches: [ next ]
+  workflow_dispatch:
+
+concurrency: prr:pre-release
+
+jobs:
+  build:
+    uses: ./.github/workflows/test.yml
+
+  publish-prerelease:
+    needs: build
+    runs-on: ubuntu-latest
+    steps:
+    - run: git clone --depth=0 https://github.com/MithrilJS/mithril.js.git && cd mithril.js
+    - uses: ./.github/actions/setup
+    - run: npm run build
+    - run: npx pr-release pr --verbose --target master --source next --compact --verbose --minimize-semver-change
+      env:
+        GITHUB_TOKEN: ${{ secrets.GH_TOKEN }}
+    # The following will publish a prerelease to npm
+    - run: echo "//registry.npmjs.org/:_authToken=$NPM_TOKEN" > ~/.npmrc
+      name: Setup NPM Auth
+      env:
+        NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
+    - run: npx pr-release infer-prerelease --preid=next --target master --source next --verbose --publish --minimize-semver-change
+      name: Publish