debug: properly dispose a debug session

fixes #57403

src/vs/workbench/parts/debug/electron-browser/debugSession.ts

@@ -432,7 +432,9 @@ export class Session implements ISession {
 
 	dispose(): void {
 		dispose(this.rawListeners);
+		this.model.clearThreads(this.getId(), true);
 		this.model.removeSession(this.getId());
+		this.fetchThreadsScheduler = undefined;
 		if (!this._raw.disconnected) {
 			this._raw.disconnect().done(undefined, errors.onUnexpectedError);
 		}