Update SDL_pixels.h

Added an opening bracket in line 520, in the comment block of SDL_PixelFormat. Simple addition to the readability of documentation.

(cherry picked from commit 03a6d98aee05aeacb4511b58e2b61dba6886874d)

include/SDL3/SDL_pixels.h

@@ -517,7 +517,7 @@ typedef enum SDL_PackedLayout
  *   ABGR32, define a platform-independent encoding into bytes in the order
  *   specified. For example, in RGB24 data, each pixel is encoded in 3 bytes
  *   (red, green, blue) in that order, and in ABGR32 data, each pixel is
- *   encoded in 4 bytes alpha, blue, green, red) in that order. Use these
+ *   encoded in 4 bytes (alpha, blue, green, red) in that order. Use these
  *   names if the property of a format that is important to you is the order
  *   of the bytes in memory or on disk.
  * - Names with a bit count per component, such as ARGB8888 and XRGB1555, are