Fix: EEVEE: Missing barrier in light sorting compute shader

At high light count, this missing barriers would
produce invalid, non-unique `prefix_sum` indices.
This then resulted in some slots inside `out_light_buf`
never written to, leaving undefined data inside them.

If the buffer was cleared to zero, these undefined light
slots would be interpreted as sun lights and the
shadow setup compute pass would critically fail because
of out of bound memory.

Fix #123195

source/blender/draw/engines/eevee_next/shaders/eevee_light_culling_sort_comp.glsl

@@ -55,6 +55,8 @@ void main()
         }
       }
     }
+
+    barrier();
   }
 
   if (valid_thread) {