This updates the script to automatically update puppet constraints so
that Puppetfile_unit is updated as well as Puppetfile. We introduced
this separate file[1] a while ago but have not been updated it
properly. Updating it periodically helps us catch up with any update
in the dependent modules more timely.
[1] 047ea125ddefa8151d6592d4772560a1b23a13dc
Depends-on: https://review.opendev.org/875301
Change-Id: I4d89a2985781f14d9ff7f76f412f0b8ccc4c6ddb
8f183d1671