Only card brand can be changed label (#4336)

## Summary
<!-- Simple summary of what was changed. -->
Added conditionally rendered footnote label for cobranded choice card
## 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. -->

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

## Changelog
<!-- Is this a notable change that affects users? If so, add a line to
`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.
-->

StripePaymentSheet/StripePaymentSheet/Resources/Localizations/en.lproj/Localizable.strings

@@ -209,6 +209,9 @@ re-entering the security code (CVV/CVC). */
 /* Text of a label for confirming an email address. E.g., 'Not [email protected]?' */
 "Not %@?" = "Not %@?";
 
+/* Text on a screen for updating a cobranded card that indicates only card brand can be changed. */
+"Only card brand can be changed." = "Only card brand can be changed.";
+
 /* Countdown timer text on a screen asking the user to approve a payment */
 "Open your UPI app to approve your payment within %@" = "Open your UPI app to approve your payment within %@";
 

StripePaymentSheet/StripePaymentSheet/Source/Categories/String+Localized.swift

@@ -119,6 +119,13 @@ extension String.Localized {
         )
     }
 
+    static var only_card_brand_can_be_changed: String {
+        STPLocalizedString(
+            "Only card brand can be changed.",
+            "Text on a screen for updating a cobranded card that indicates only card brand can be changed."
+        )
+    }
+
     static var save: String {
        STPLocalizedString(
            "Save",

StripePaymentSheet/StripePaymentSheet/Source/PaymentSheet/ViewControllers/UpdatePaymentMethodViewController.swift

@@ -125,7 +125,7 @@ final class UpdatePaymentMethodViewController: UIViewController {
     }()
 
     private lazy var footnoteLabel: UITextView? = {
-        if viewModel.canEdit || viewModel.errorState {
+        if viewModel.errorState {
             return nil
         }
         let label = ElementsUI.makeSmallFootnote(theme: viewModel.appearance.asElementsTheme)

StripePaymentSheet/StripePaymentSheet/Source/PaymentSheet/ViewControllers/UpdatePaymentMethodViewModel.swift

@@ -41,7 +41,7 @@ class UpdatePaymentMethodViewModel {
     lazy var footnote: String = {
         switch paymentMethod.type {
         case .card:
-            return .Localized.card_details_cannot_be_changed
+            return canEdit ? .Localized.only_card_brand_can_be_changed : .Localized.card_details_cannot_be_changed
         case .USBankAccount:
             return .Localized.bank_account_details_cannot_be_changed
         case .SEPADebit: