Bug#972371: debian-reference: Add CI to ensure that git is buildable

[肖盛文]

hi,Stuart,

   I had add make entity CI in pipeline, but meet the errors, please 
help see:

https://salsa.debian.org/debian/debian-reference/-/jobs/1084031

Connecting to popcon.debian.org (popcon.debian.org)|209.87.16.63|:443... 
connected.
|
ERROR: The certificate of 'popcon.debian.org' is not trusted.
||ERROR: The certificate of 'popcon.debian.org' doesn't have a known 
issuer.|

Could you help to add |'popcon.debian.org' into trusted?|

Thanks!

xiao sheng wen