Another adaptation for jupyter-collaboration 4.x

I don't know why I'm making this change, I just cribbed it from here:

<jupyterlab/jupyter-chat@2b688d7#diff-8fc8f31371b7227cd359debf0e0c3a1c7da5718d36d541185c4f9e029be9ef3b>

Author: mfisher87

python/jupytergis_qgis/src/plugins.ts

@@ -262,7 +262,7 @@ const activate = async (
 
         // Check if the file exists
         let fileExist = true;
-        await drive.get(absolutePath, { content: false }).catch(() => {
+        await app.serviceManager.contents.get(absolutePath, { content: false }).catch(() => {
           fileExist = false;
         });
         if (fileExist) {