fix(iOS): Properly retain/release backgroundColor in RCTBorderDrawing (#46797)

Summary:
I discovered this while working on my shim of `UIGraphicsImageRenderer` for macOS (See https://github.com/microsoft/react-native-macos/pull/2209). A variable of type`CGColorRef` is not automatically retained and released when passed into a block. There was a case in `RCTBorderDrawing` where we were doing so. To fix this, we have two options:

1. Pass a `UIColor` instead (Requires a change to the signature of the function calling it)
2. Properly retain and release the variable.

The first option would technically be a breaking change (we would need to change the signature of `RCTGetBorderImage`, so I'm opting for option 2.

## Changelog:

[IOS] [FIXED] -  Properly retain/release backgroundColor in RCTBorderDrawing

Pull Request resolved: https://github.com/facebook/react-native/pull/46797

Test Plan: CI should pass. Locally, borders still draw fine for me.

Reviewed By: joevilches

Differential Revision: D63827824

Pulled By: cipolleschi

fbshipit-source-id: 926601d062b90a7d741d7a1af3070cec4b8795ae

packages/react-native/React/Views/RCTBorderDrawing.m

@@ -232,6 +232,8 @@ static UIImage *RCTGetSolidBorderImage(
 
   UIGraphicsImageRenderer *const imageRenderer =
       RCTMakeUIGraphicsImageRenderer(size, backgroundColor, hasCornerRadii, drawToEdge);
+
+  CGColorRetain(backgroundColor);
   UIImage *image = [imageRenderer imageWithActions:^(UIGraphicsImageRendererContext *_Nonnull rendererContext) {
     const CGContextRef context = rendererContext.CGContext;
     const CGRect rect = {.size = size};
@@ -242,6 +244,7 @@ static UIImage *RCTGetSolidBorderImage(
       CGContextAddPath(context, path);
       CGContextFillPath(context);
     }
+    CGColorRelease(backgroundColor);
 
     CGContextAddPath(context, path);
     CGPathRelease(path);