[examples] fix: use quotation marks when including raylib.h (#4821)

...so it will always prioritize local version of raylib instead of
system-wide installations, which is a huge problem when testing any
changes done locally to raylib as it might cause silent mismatch issues.
There were only 4 examples affected by this issue which were using
`#include <raylib.h>`. Other examples use proper `#include "raylib.h"`

Fixes: https://github.com/raysan5/raylib/issues/4820

examples/shapes/shapes_draw_circle_sector.c

@@ -15,7 +15,7 @@
 *
 ********************************************************************************************/
 
-#include <raylib.h>
+#include "raylib.h"
 
 #define RAYGUI_IMPLEMENTATION
 #include "raygui.h"                 // Required for GUI controls

examples/shapes/shapes_draw_rectangle_rounded.c

@@ -15,7 +15,7 @@
 *
 ********************************************************************************************/
 
-#include <raylib.h>
+#include "raylib.h"
 
 #define RAYGUI_IMPLEMENTATION
 #include "raygui.h"                 // Required for GUI controls

examples/shapes/shapes_draw_ring.c

@@ -15,7 +15,7 @@
 *
 ********************************************************************************************/
 
-#include <raylib.h>
+#include "raylib.h"
 
 #define RAYGUI_IMPLEMENTATION
 #include "raygui.h"                 // Required for GUI controls

examples/textures/textures_image_channel.c

@@ -17,7 +17,7 @@
 *
 ********************************************************************************************/
 
-#include <raylib.h>
+#include "raylib.h"
 
 //------------------------------------------------------------------------------------
 // Program main entry point