LibGfx: Store Core::Resources in RefPtr to const

Author: https://github.com/ADKaster
Commit: ffd0259bef
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4362
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/Hendiadyoin1

Libraries/LibGfx/Font/FontData.cpp

@@ -32,7 +32,7 @@ FontData::FontData(ByteBuffer&& byte_buffer)
 {
 }
 
-FontData::FontData(NonnullRefPtr<Core::Resource> resource)
+FontData::FontData(NonnullRefPtr<Core::Resource const> resource)
     : m_data(move(resource))
 {
 }