metal: fixed reading textures with format SDL_PIXELFORMAT_RGBA128_FLOAT

(cherry picked from commit 113e97e193479c137b3f5ba166b7ab37e0ed8219)

src/render/metal/SDL_render_metal.m

@@ -1975,6 +1975,9 @@ static SDL_Surface *METAL_RenderReadPixels(SDL_Renderer *renderer, const SDL_Rec
         case MTLPixelFormatRGBA16Float:
             format = SDL_PIXELFORMAT_RGBA64_FLOAT;
             break;
+        case MTLPixelFormatRGBA32Float:
+            format = SDL_PIXELFORMAT_RGBA128_FLOAT;
+            break;
         case MTLPixelFormatB5G6R5Unorm:
             format = SDL_PIXELFORMAT_RGB565;
             break;