fix(template-devops-requirements): tweak index-url for renovatebot

Renovatebot should understand --index-url in requirements.txt files but the renovatebot docs[1] explicitly call out that it needs to be the first line. Our files have it as the first effective line after comments but, to be pedantic, it's not the first physical line. Update the --index-url usage to match the renovatebot docs.

[1] https://docs.renovatebot.com/python/#index-url-in-requirementstxt