fix(cdk/accordion): resolve changed after checked error

Fixes a "changed after checked" error in the expansion panel due to the header depending on the `disabled` value of the expansion panel.

(cherry picked from commit 0612c6a)

Author: crisbeto

goldens/cdk/accordion/index.api.md

@@ -44,7 +44,8 @@ export class CdkAccordionItem implements OnInit, OnDestroy {
     close(): void;
     readonly closed: EventEmitter<void>;
     readonly destroyed: EventEmitter<void>;
-    disabled: boolean;
+    get disabled(): boolean;
+    set disabled(value: boolean);
     get expanded(): boolean;
     set expanded(expanded: boolean);
     readonly expandedChange: EventEmitter<boolean>;

src/cdk/accordion/accordion-item.ts

@@ -16,6 +16,7 @@ import {
   booleanAttribute,
   inject,
   OnInit,
+  signal,
 } from '@angular/core';
 import {_IdGenerator} from '../a11y';
 import {UniqueSelectionDispatcher} from '../collections';
@@ -90,7 +91,14 @@ export class CdkAccordionItem implements OnInit, OnDestroy {
   private _expanded = false;
 
   /** Whether the AccordionItem is disabled. */
-  @Input({transform: booleanAttribute}) disabled: boolean = false;
+  @Input({transform: booleanAttribute})
+  get disabled() {
+    return this._disabled();
+  }
+  set disabled(value: boolean) {
+    this._disabled.set(value);
+  }
+  private _disabled = signal(false);
 
   /** Unregister function for _expansionDispatcher. */
   private _removeUniqueSelectionListener: () => void = () => {};

src/material/expansion/accordion.spec.ts

@@ -5,13 +5,7 @@ import {
   dispatchEvent,
   dispatchKeyboardEvent,
 } from '@angular/cdk/testing/private';
-import {
-  Component,
-  provideCheckNoChangesConfig,
-  QueryList,
-  ViewChild,
-  ViewChildren,
-} from '@angular/core';
+import {Component, QueryList, ViewChild, ViewChildren} from '@angular/core';
 import {TestBed, waitForAsync} from '@angular/core/testing';
 import {By} from '@angular/platform-browser';
 import {
@@ -25,18 +19,6 @@ describe('MatAccordion', () => {
   let focusMonitor: FocusMonitor;
 
   beforeEach(waitForAsync(() => {
-    TestBed.configureTestingModule({
-      providers: [provideCheckNoChangesConfig({exhaustive: false})],
-      imports: [
-        MatExpansionModule,
-        AccordionWithHideToggle,
-        AccordionWithTogglePosition,
-        NestedPanel,
-        SetOfItems,
-        NestedAccordions,
-      ],
-    });
-
     focusMonitor = TestBed.inject(FocusMonitor);
   }));