Copilot: correctly cleanup compression timer

fixes a leak and a crash if the timer triggers after the widget was
deleted.

Change-Id: I57794009186d4c5e4dee0b0c0746ffc5468000b7
Reviewed-by: Artem Sokolovskii <artem.sokolovskii@qt.io>
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/copilot/copilotclient.h

@@ -50,6 +50,7 @@ private:
     QMap<TextEditor::TextEditorWidget *, GetCompletionRequest> m_runningRequests;
     struct ScheduleData
     {
+        ~ScheduleData();
         int cursorPosition = -1;
         QTimer *timer = nullptr;
     };