Small changes to ui tests (#4214)

## Summary
<!-- Simple summary of what was changed. -->


## Motivation
<!-- Why are you making this change? If it's for fixing a bug, if
possible, please include a code snippet or example project that
demonstrates the issue. -->
Attempt to mitigate tests testCVCRecollectionComplete_deferredCSC and
testPaymentSheetSwiftUI that failed initially but passed on retry in the
CI

## Testing
<!-- How was the code tested? Be as specific as possible. -->

## Changelog
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`CHANGELOG.md` and prefix the line with one of the following:
    - [Added] for new features.
    - [Changed] for changes in existing functionality.
    - [Deprecated] for soon-to-be removed features.
    - [Removed] for now removed features.
    - [Fixed] for any bug fixes.
    - [Security] in case of vulnerabilities.
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Example/PaymentSheet Example/PaymentSheetUITest/PaymentSheetUITest.swift

@@ -306,7 +306,8 @@ class PaymentSheetStandardUITests: PaymentSheetUITestCase {
         buyButton.forceTapElement()
 
         try! fillCardData(app)
-        app.buttons["Pay €9.73"].tap()
+        app.buttons["Done"].waitForExistenceAndTap(timeout: 3.0)
+        app.buttons["Pay €9.73"].waitForExistenceAndTap(timeout: 3.0)
         let successText = app.staticTexts["Payment status view"]
         XCTAssertTrue(successText.waitForExistence(timeout: 10.0))
         XCTAssertNotNil(successText.label.range(of: "Success!"))
@@ -1634,9 +1635,7 @@ class PaymentSheetCVCRecollectionUITests: PaymentSheetUITestCase {
         saveThisCardToggle.tap()
         XCTAssertTrue(saveThisCardToggle.isSelected)
 
-        let payButton = app.buttons["Pay $50.99"]
-        XCTAssert(payButton.isEnabled)
-        payButton.tap()
+        app.buttons["Pay $50.99"].waitForExistenceAndTap(timeout: 5.0)
 
         let successText = app.staticTexts["Success!"]
         XCTAssertTrue(successText.waitForExistence(timeout: 10.0))