Clear background and reusing window

[Hoderu]

Describe the bug
It is a bug connected with transparent navigation bar color. And so we can see the layers below.

To Reproduce
Steps to reproduce the behavior:

1. Install version 2.1.0 of KlarnaMobileSDK
2. Update Xcode to version 13.0
3. Open Pay now option
4. Choose "Terms for the Klarna Shopping Sevice"
5. See clear UINavigationBar color inside ProgressNavigationController

Expected behavior
A solid color, for example: white.
Or color related with system theme.

Screenshots

Device and version:

• Device: iPhone 13 Pro Max
• OS version: iOS 15.0
• Klarna In-App SDK version 2.1.0

Merchant Name
I'd rather not state this here unless absolutely necessary.

Impact Level
This is an unpleasant mistake for which I had to make a workaround using UIAppearance.

Additional context
While I was researching the problem, I found another minor issue.
If we open and close the "Terms for the Klarna Shopping Sevice" multiple times we will see a lot of extra windows inside UIWindowScene.windows array:
<__NSArrayM 0x600003dda250>( <KlarnaMobileSDK.KlarnaWindow: 0x7fd410f12590; baseClass = UIWindow; frame = (0 0; 428 926); hidden = YES; gestureRecognizers = <NSArray: 0x600003997e70>; layer = <UIWindowLayer: 0x6000039959b0>>,

<KlarnaMobileSDK.KlarnaWindow: 0x7fd41206c970; baseClass = UIWindow; frame = (0 0; 428 926); hidden = YES; gestureRecognizers = <NSArray: 0x600007a9fea0>; layer = <UIWindowLayer: 0x600007a9ec10>>,

<KlarnaMobileSDK.KlarnaWindow: 0x7fd3fa9977f0; baseClass = UIWindow; frame = (0 0; 428 926); hidden = YES; gestureRecognizers = <NSArray: 0x60000a7aa4c0>; layer = <UIWindowLayer: 0x60000a7a9cb0>>,

<KlarnaMobileSDK.KlarnaWindow: 0x7fd3cd631670; baseClass = UIWindow; frame = (0 0; 428 926); gestureRecognizers = <NSArray: 0x60000bcdc3c0>; layer = <UIWindowLayer: 0x60000bcde280>>, …

I think there is a bug that every time a new window is created instead of reusing the old one.