[CI] Fix gitian script path

Summary:
The gitian build configurations were not migrated after D8821, I missed
the template.

Test Plan:

./contrib/teamcity/build-configurations.py gitian-osx # can be any OS

Reviewers: #bitcoin_abc, PiRK, majcosta

Reviewed By: #bitcoin_abc, PiRK, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8844