fix(module:icon): resolve memory leak (#6839)

components/icon/icon.service.ts

@@ -5,9 +5,9 @@
 
 import { DOCUMENT } from '@angular/common';
 import { HttpBackend } from '@angular/common/http';
-import { Inject, Injectable, InjectionToken, Optional, RendererFactory2, Self } from '@angular/core';
+import { Inject, Injectable, InjectionToken, OnDestroy, Optional, RendererFactory2, Self } from '@angular/core';
 import { DomSanitizer } from '@angular/platform-browser';
-import { Subject } from 'rxjs';
+import { Subject, Subscription } from 'rxjs';
 
 import { IconDefinition, IconService } from '@ant-design/icons-angular';
 
@@ -31,10 +31,18 @@ export const DEFAULT_TWOTONE_COLOR = '#1890ff';
 @Injectable({
   providedIn: 'root'
 })
-export class NzIconService extends IconService {
+export class NzIconService extends IconService implements OnDestroy {
   configUpdated$ = new Subject<void>();
 
   private iconfontCache = new Set<string>();
+  private subscription: Subscription | null = null;
+
+  ngOnDestroy(): void {
+    if (this.subscription) {
+      this.subscription.unsubscribe();
+      this.subscription = null;
+    }
+  }
 
   normalizeSvgElement(svg: SVGElement): void {
     if (!svg.getAttribute('viewBox')) {
@@ -81,7 +89,7 @@ export class NzIconService extends IconService {
   }
 
   private onConfigChange(): void {
-    this.nzConfigService.getConfigChangeEventForComponent('icon').subscribe(() => {
+    this.subscription = this.nzConfigService.getConfigChangeEventForComponent('icon').subscribe(() => {
       this.configDefaultTwotoneColor();
       this.configDefaultTheme();
       this.configUpdated$.next();