fix(ui5-dynamic-page): update header sticky on manual snap (#10431)

Prevent header glitch when unsnapping after manual snap and scroll

When the header was manually snapped before scrolling, the sticky area
state wasn't properly updated, causing visual glitches during unsnap.

Fixes: #10430

packages/fiori/src/DynamicPage.ts

@@ -326,6 +326,10 @@ class DynamicPage extends UI5Element {
 		const headerHeight = this.dynamicPageHeader.getBoundingClientRect().height;
 		const lastHeaderSnapped = this._headerSnapped;
 
+		if (this._headerSnapped && scrollTop > headerHeight) {
+			this.showHeaderInStickArea = false;
+		}
+
 		const shouldSnap = !this._headerSnapped && scrollTop > headerHeight + SCROLL_THRESHOLD;
 		const shouldExpand = this._headerSnapped && (scrollTop < headerHeight - SCROLL_THRESHOLD
 			|| (!scrollTop && !headerHeight));