add test file for message box

src/test_box.zig

@@ -0,0 +1,23 @@
+const std = @import("std");
+const r = @import("raylib.zig");
+
+pub fn main() anyerror!void {
+    r.InitWindow(800, 450, "doggo");
+    defer r.CloseWindow();
+
+    while (!r.WindowShouldClose()) {
+
+        // Draw
+        r.BeginDrawing();
+        defer r.EndDrawing();
+
+        r.ClearBackground(r.RAYWHITE);
+
+        _ = r.GuiMessageBox(
+            r.Rectangle{ .x = 0, .y = 0, .width = 200, .height = 200 },
+            "Message Box Title",
+            "Message content",
+            null,
+        );
+    }
+}