Fix flaky anvil-catalog filter deselection test (#4771)

* Initial plan

* fix(e2e): use name-based locator in selectFirstOption to avoid flakiness

Agent-Logs-Url: https://github.com/DataBiosphere/data-browser/sessions/4f68d6fe-5720-4897-8b51-8b219e4687d6

Co-authored-by: frano-m <18710366+frano-m@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: frano-m <18710366+frano-m@users.noreply.github.com>

Author: Copilot

e2e/anvil-catalog/anvilcatalog-filters.spec.ts

@@ -242,6 +242,19 @@ async function openFilterDropdown(
   await expectFilterPopoverOpen(filters.page());
 }
 
+/**
+ * Returns a locator for a named filter item in the open filter popover.
+ * @param page - Page.
+ * @param optionName - The display name of the filter option.
+ * @returns A locator for the matching filter item.
+ */
+function namedPopoverFilterItem(page: Page, optionName: string): Locator {
+  return filterPopover(page)
+    .getByTestId(TEST_IDS.FILTER_ITEM)
+    .filter({ hasText: new RegExp(`^${escapeRegExp(optionName)}\\s*\\d+\\s*`) })
+    .first();
+}
+
 /**
  * Opens a sidebar filter dropdown, selects its first option, and returns the
  * option name. Waits for the item to be selected before returning.
@@ -260,7 +273,10 @@ async function selectFirstOption(
   const name = await extractOptionName(option);
   await expectFilterItemNotSelected(option);
   await option.click();
-  await expectFilterItemSelected(option);
+  // Re-locate by name rather than position since the list may re-sort after
+  // selection, causing the positional `.first()` locator to resolve to a
+  // different (non-selected) element.
+  await expectFilterItemSelected(namedPopoverFilterItem(page, name));
   await page.keyboard.press(KEYBOARD_KEYS.ESCAPE);
   await expectFilterPopoverClosed(page);
   return name;