fix(uitests): replace illegal key path with a closure in quickDiagnostics

'.map(\.label)' failed to build: XCUIElement.label is @MainActor-isolated,
and a bare key path literal must be formable from any isolation context,
which a main-actor-isolated property can't satisfy. This was a hard
compiler error (not just a concurrency warning), and it cascaded into a
flood of secondary diagnostics across the whole file/batch compile unit,
obscuring the actual cause. Replaced with a closure ('{ $0.label }'),
which isn't subject to that restriction.

PediFoodsUITests/CartCheckoutFlowTests.swift

@@ -39,9 +39,12 @@ final class CartCheckoutFlowTests: XCTestCase {
         if errorText.exists {
             signals.append("error text visible: \(errorText.label)")
         }
+        // A bare `\.label` key path literal is illegal here - `label` is
+        // @MainActor-isolated, and a key path must be formable from any
+        // isolation context. A closure isn't subject to that restriction.
         let visibleTexts = app.staticTexts.allElementsBoundByIndex
             .prefix(15)
-            .map(\.label)
+            .map { $0.label }
             .joined(separator: " | ")
         signals.append("visible static texts: [\(visibleTexts)]")
         return signals.joined(separator: "; ")