[release/10.0] Fix flaky CanElevateEffectiveMaxItemCount_WhenOverscanExceedsMax (#67705)

Backport of #66291 to release/10.0.

The test was flaky because GetVisibleItemIndices() was called once and the
result was reused in all Browser.True() retry loops and across PageDown
iterations. In server mode, the async virtualization update had not finished
yet when the snapshot was taken, so the retry loops kept checking a stale list
that never reached 200 items.

Fix by re-querying GetVisibleItemIndices() inside each Browser.True() loop so
retries see the current DOM state.

This fix was already made on main via #66291 but was never backported to
release/10.0, where the test is still flaking in the components-e2e pipeline.

Co-authored-by: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

src/Components/test/E2ETest/Tests/VirtualizationTest.cs

@@ -578,9 +578,14 @@ public void CanElevateEffectiveMaxItemCount_WhenOverscanExceedsMax()
     {
         Browser.MountTestComponent<VirtualizationLargeOverscan>();
         var container = Browser.Exists(By.Id("virtualize-large-overscan"));
-        // Ensure we have an initial contiguous batch and the elevated effective max has kicked in (>= OverscanCount)
-        var indices = GetVisibleItemIndices();
-        Browser.True(() => indices.Count >= 200);
+        // Wait for the elevated effective max to kick in (>= OverscanCount).
+        // Re-query inside the retry loop so we see new items as they render.
+        List<int> indices = null;
+        Browser.True(() =>
+        {
+            indices = GetVisibleItemIndices();
+            return indices.Count >= 200;
+        });
 
         // Give focus so PageDown works
         container.Click();
@@ -595,8 +600,13 @@ public void CanElevateEffectiveMaxItemCount_WhenOverscanExceedsMax()
         var scrollTop = (long)js.ExecuteScript("return arguments[0].scrollTop", container);
         while (scrollTop + clientHeight < scrollHeight)
         {
-            // Validate contiguity on the current page
-            Browser.True(() => IsCurrentViewContiguous(indices));
+            // Re-query visible items after each scroll so contiguity and
+            // progress checks reflect the current DOM state.
+            Browser.True(() =>
+            {
+                indices = GetVisibleItemIndices();
+                return IsCurrentViewContiguous(indices);
+            });
 
             // Track progress in indices
             var currentMax = indices.Max();