fix(modal): backdrop animation when backdropBreakpoint is 1 (#25430)

Resolves #25402

core/src/components/modal/utils.spec.ts

@@ -0,0 +1,11 @@
+import { getBackdropValueForSheet } from './utils';
+
+describe('getBackdropValueForSheet()', () => {
+  it('should return a valid integer when backdropBreakpoint is 1', () => {
+    /**
+     * Issue: https://github.com/ionic-team/ionic-framework/issues/25402
+     */
+    const backdropBreakpoint = 1;
+    expect(getBackdropValueForSheet(1, backdropBreakpoint)).toBe(0);
+  });
+});