Fix typos in source code using codespell

From https://github.com/lucasdemarchi/codespell

editor/plugins/texture_region_editor_plugin.cpp

@@ -710,7 +710,7 @@ void TextureRegionEditor::_edit_region() {
 											autoslice_cache.erase(F->next());
 										} else {
 											queue_erase = true;
-											//Cant delete the first rect in the list.
+											//Can't delete the first rect in the list.
 										}
 										merged = true;
 									}