timeline: fix memory leak when toggling pane visibility (microsoft#304668)

* timeline: dispose previous visibility subscriptions before recreating

* retrigger CI

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Co-authored-by: Raymond Zhao <7199958+rzhao271@users.noreply.github.com>

Author: xingsy97

src/vs/workbench/contrib/timeline/browser/timelinePane.ts

@@ -883,6 +883,7 @@ export class TimelinePane extends ViewPane {
 	override setVisible(visible: boolean): void {
 		if (visible) {
 			this.extensionService.activateByEvent('onView:timeline');
+			this.visibilityDisposables?.dispose();
 			this.visibilityDisposables = new DisposableStore();
 
 			this.editorService.onDidActiveEditorChange(this.onActiveEditorChanged, this, this.visibilityDisposables);