Varnish Cache has been renamed to Vinyl Cache

More info here:
https://vinyl-cache.org/
https://vinyl-cache.org/organization/on_vinyl_cache_and_varnish_cache.html#org-vinyl-varnish

Upgrade guide:
https://vinyl-cache.org/docs/9.0/whats-new/upgrading-9.0.html

Start by searching the repository for references to Varnish Cache, then read the linked Vinyl Cache information and upgrade guide. Done means the relevant references and integration remain compatible with the renamed project, but the issue does not identify specific files or tests.

Written by the indexing model from the issue text.