fix: Incompatibility with older versions of Jupyter

- We're accessing a private _context property, wrap it in a try/catch and just warn if there's an error
- Tested against notebook 6.5.6
```sh
pip install deephaven-server notebook==6.5.6 jupyterlab
pip install -e ".[test, examples]"
jupyter notebook
```

Then running in the Jupyter notebook:
```
from deephaven_server import Server
s = Server(jvm_args=["-Dauthentication.psk=iris"])
s.start()

from deephaven import empty_table
from deephaven_ipywidgets import DeephavenWidget
t = empty_table(1000).update("x=i")
display(DeephavenWidget(t))
```

src/widget.ts

@@ -63,24 +63,32 @@ export class DeephavenView extends DOMWidgetView {
   constructor(options: Backbone.ViewOptions<DeephavenModel>) {
     super(options);
 
+    this.initKernelListeners();
+  }
+
+  initKernelListeners(): void {
     this.model.on(
       'change:kernel_active',
       () => this.onDisconnect('exiting'),
       this
     );
 
-    // This uses the private _context property, but it's the only way to get
-    // the session context. These context listeners are used to listen to
-    // kernel events. See this file for examples within jupyter kernel:
-    // https://github.com/jupyter-widgets/ipywidgets/blob/47058a373d2c2b3acf101677b2745e14b76dd74b/python/jupyterlab_widgets/src/manager.ts#L427
-    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
-    // @ts-ignore
-    // eslint-disable-next-line no-underscore-dangle
-    this.context = this.model.widget_manager._context;
-    this.context.sessionContext.statusChanged.connect(
-      this.onRestartOrTerminate,
-      this
-    );
+    try {
+      // This uses the private _context property, but it's the only way to get
+      // the session context. These context listeners are used to listen to
+      // kernel events. See this file for examples within jupyter kernel:
+      // https://github.com/jupyter-widgets/ipywidgets/blob/47058a373d2c2b3acf101677b2745e14b76dd74b/python/jupyterlab_widgets/src/manager.ts#L427
+      // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+      // @ts-ignore
+      // eslint-disable-next-line no-underscore-dangle
+      this.context = this.model.widget_manager._context;
+      this.context.sessionContext.statusChanged.connect(
+        this.onRestartOrTerminate,
+        this
+      );
+    } catch (e) {
+      log.warn('Failed to add kernel listeners', e);
+    }
   }
 
   sendAuthenticationResponse = (