LibGL: Fix minor const-correctness issues

Userland/Libraries/LibGL/Shaders/Program.cpp

@@ -57,7 +57,7 @@ ErrorOr<void> Program::link(GPU::Device& device)
     // Link vertex shader objects
 
     Vector<GLSL::ObjectFile const*> vertex_shader_object_files;
-    for (auto vertex_shader : m_vertex_shaders)
+    for (auto const& vertex_shader : m_vertex_shaders)
         vertex_shader_object_files.append(vertex_shader->object_file());
 
     auto linked_vertex_shader_or_error = linker.link(vertex_shader_object_files);

Userland/Libraries/LibGL/Shaders/Program.h

@@ -32,13 +32,13 @@ public:
 
 private:
     bool m_link_status { false };
-    Vector<NonnullRefPtr<Shader>> m_vertex_shaders;
-    Vector<NonnullRefPtr<Shader>> m_fragment_shaders;
+    Vector<NonnullRefPtr<Shader const>> m_vertex_shaders;
+    Vector<NonnullRefPtr<Shader const>> m_fragment_shaders;
     Optional<String> m_info_log;
     OwnPtr<GLSL::LinkedShader> m_linked_vertex_shader;
     OwnPtr<GLSL::LinkedShader> m_linked_fragment_shader;
-    RefPtr<GPU::Shader> m_gpu_vertex_shader;
-    RefPtr<GPU::Shader> m_gpu_fragment_shader;
+    RefPtr<GPU::Shader const> m_gpu_vertex_shader;
+    RefPtr<GPU::Shader const> m_gpu_fragment_shader;
 };
 
 }