Composer accessing 2nd repo (shared code) wastes 1 minute reading ALL versions of repo's composer.json

Building AWS website that uses a second repo which contains code common to multiple websites.

“Composer GH authentication and install” step now takes 55 seconds - and that time is growing slightly each time we tag another release of the second repo.

While job is running, can visually see that most of that time passes while emitting lines like:
“Reading composer.json of …shared (2.18.37)”,
and so on, down to the very first tag.

How avoid this extra time?