Upgrade actions/upload-artifact to v3

This upgrades the action to remove a deprecation warning about Node 12.

.github/workflows/main.yml

@@ -47,7 +47,7 @@ jobs:
           cp dist/*.vsix artifacts
 
       - name: Upload artifacts
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v3
         if: matrix.os == 'ubuntu-latest'
         with:
           name: vscode-codeql-extension