chore: fix autocomplete test (#7743)

Due to 9b4f435#diff-295d2cf77570f5880fd0c828fe60c2c4 the `mat-disabled` class is no longer being added to the underline element.

The disabled class is now being added to the host element of the `mat-form-field` component.

Author: devversion

src/lib/autocomplete/autocomplete.spec.ts

@@ -543,20 +543,20 @@ describe('MatAutocomplete', () => {
     }));
 
     it('should disable input in view when disabled programmatically', () => {
-      const inputUnderline =
-          fixture.debugElement.query(By.css('.mat-form-field-underline')).nativeElement;
+      const formFieldElement =
+          fixture.debugElement.query(By.css('.mat-form-field')).nativeElement;
 
       expect(input.disabled)
           .toBe(false, `Expected input to start out enabled in view.`);
-      expect(inputUnderline.classList.contains('mat-disabled'))
+      expect(formFieldElement.classList.contains('mat-form-field-disabled'))
           .toBe(false, `Expected input underline to start out with normal styles.`);
 
       fixture.componentInstance.stateCtrl.disable();
       fixture.detectChanges();
 
       expect(input.disabled)
           .toBe(true, `Expected input to be disabled in view when disabled programmatically.`);
-      expect(inputUnderline.classList.contains('mat-disabled'))
+      expect(formFieldElement.classList.contains('mat-form-field-disabled'))
           .toBe(true, `Expected input underline to display disabled styles.`);
     });