I’m not exactly sure how you’re trying to use this, but a few options would be:
First Option
to use their addon cli called newman. You can run collections from a URL or Local file with newman using
newman run http://some.url.here
Then if you make the remote url a part of a git repository it would obviously update/change with each commit/pull
Second Option
Try this with extreme caution and only if you feel comfortable with the process, also this may not be compliant with their terms of use so I don’t suggest you try it without first some research
If you can find the directory in which the Postman collections are held, you could create a hard link with the command line from a git repository on your machine to the directory or specific file you need to link. Whenever you change the source file the one in the Postman config will change.
The way in which you accomplish this will depend on the system you use and version of Postman.