Update GitHub actions to the latest version

This includes the update of the Node.js version used. The action
`GabrielBB/xvfb-action` is deprecated and is no longer needed.

.github/workflows/main.yml

@@ -9,26 +9,23 @@ jobs:
         os: [macos-latest, ubuntu-latest, windows-latest]
     runs-on: ${{matrix.os}}
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
-          node-version: 16
+          node-version: 20
       - run: npm install
-      - name: test
-        uses: GabrielBB/[email protected]
-        with:
-          run: npm test
+      - run: xvfb-run npm test
 
   package:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
-          node-version: 16
+          node-version: 20
       - run: npm install
       - run: npx vsce package
-      - uses: actions/upload-artifact@v3
+      - uses: actions/upload-artifact@v4
         with:
           name: vscode-remark.vsix
           path: '*.vsix'

.github/workflows/publish.yml

@@ -8,10 +8,10 @@ jobs:
   publish:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
-          node-version: 16
+          node-version: 20
       - run: npm install
       - run: npx vsce package
       - run: npx vsce publish --packagePath *.vsix