refactor(overlays): update code order and add GH issue

Author: thetaPC

core/src/utils/overlays.ts

@@ -650,10 +650,6 @@ export const dismiss = async <OverlayDismissOptions>(
 
   const isLastOverlay = presentedOverlays.length === 1;
 
-  if (isLastOverlay) {
-    document.body.classList.remove(BACKDROP_NO_SCROLL);
-  }
-
   /**
    * For accessibility, toasts lack focus traps and don’t receive
    * `aria-hidden` on the root element when presented.
@@ -677,6 +673,10 @@ export const dismiss = async <OverlayDismissOptions>(
     setRootAriaHidden(false);
   }
 
+  if (isLastOverlay) {
+    document.body.classList.remove(BACKDROP_NO_SCROLL);
+  }
+
   overlay.presented = false;
 
   try {

core/src/utils/test/overlays/overlays-scroll-blocking.spec.ts

@@ -87,6 +87,7 @@ describe('overlays: scroll blocking', () => {
     expect(body).not.toHaveClass('backdrop-no-scroll');
   });
 
+  // Fixes https://github.com/ionic-team/ionic-framework/issues/30112
   it('should not enable scroll until last toast overlay is dismissed', async () => {
     const page = await newSpecPage({
       components: [Toast],