script-fu: mark label for translation
Small i18n followup to the port to GimpProcedureDialog for carve-it.scm in 165f616f
I found the port exposes a string "Mask drawable" to the dialog. The string has existed for many years but not been used in the dialog, and is not translated.
Marking as translatable means a string break, but I think translators will have enough time before 3.0 if we announce it on Discourse.
Leaving the decision to @Jehan :-)