Code quality: Fix header guards consistency

Adds `header_guards.sh` bash script, used in CI to validate future
changes. Can be run locally to fix invalid header guards.

modules/gltf/structures/gltf_accessor.h

@@ -101,4 +101,5 @@ public:
 	int get_sparse_values_byte_offset();
 	void set_sparse_values_byte_offset(int p_sparse_values_byte_offset);
 };
+
 #endif // GLTF_ACCESSOR_H

modules/gltf/structures/gltf_animation.h

@@ -71,4 +71,5 @@ private:
 	bool loop = false;
 	HashMap<int, Track> tracks;
 };
+
 #endif // GLTF_ANIMATION_H

modules/gltf/structures/gltf_buffer_view.h

@@ -65,4 +65,5 @@ public:
 	void set_indices(bool p_indices);
 	// matrices need to be transformed to this
 };
+
 #endif // GLTF_BUFFER_VIEW_H

modules/gltf/structures/gltf_camera.h

@@ -55,4 +55,5 @@ public:
 	float get_depth_near() const { return depth_near; }
 	void set_depth_near(float p_val) { depth_near = p_val; }
 };
+
 #endif // GLTF_CAMERA_H

modules/gltf/structures/gltf_node.h

@@ -97,4 +97,5 @@ public:
 	GLTFLightIndex get_light();
 	void set_light(GLTFLightIndex p_light);
 };
+
 #endif // GLTF_NODE_H

modules/gltf/structures/gltf_skeleton.h

@@ -98,4 +98,5 @@ public:
 
 	int32_t get_bone_attachment_count();
 };
+
 #endif // GLTF_SKELETON_H

modules/gltf/structures/gltf_skin.h

@@ -106,4 +106,5 @@ public:
 	Ref<Skin> get_godot_skin();
 	void set_godot_skin(Ref<Skin> p_godot_skin);
 };
+
 #endif // GLTF_SKIN_H