Don't reload release notes when clicking on tab

Fixes #15214

**bug**
release notes reloaded when clicking on the tab again

**Fix**
Like with the html preview, only reload contents of the release notes view if the contents are actually different

src/vs/workbench/parts/update/electron-browser/releaseNotesEditor.ts

@@ -58,6 +58,10 @@ export class ReleaseNotesEditor extends BaseEditor {
 	}
 
 	setInput(input: ReleaseNotesInput, options: EditorOptions): TPromise<void> {
+		if (this.input && this.input.matches(input)) {
+			return TPromise.as(undefined);
+		}
+
 		const { text } = input;
 
 		this.contentDisposables = dispose(this.contentDisposables);