In your local FP working copy, after pulling the commit the update package should target to:

git archive -o ../12to13.zip HEAD $(git diff --name-only 9ce0674b577d2eb23ce66203a4ef74848c1cfe38 --diff-filter=ACMRTUXB)

(whereas 9ce0674b577d2eb23ce66203a4ef74848c1cfe38 is the commit ID of the FP release the update package should be working on)