CI cache does not work correctly for branches

Since moving the cache priming into the request stage in #37028 - caches are broken for non `main` branches

the reason for this is that the request stage runs in the context of the target branch, whereas the actual runs always run in the context of `main`, and the cache is scoped to the context

for PRs/pushes to `main` the context is the same so no issue, for release branches - eg release/v.* the cache is scoped to that branch and so when the ci runs in `main` context it is not within its scope (fwiw it would work the other way round as `main` is higher scoped than the release branch)

the caches currently work only because they were created before the change - and so retain the higher `main` scope

there is not an easy fix for this and it has highlighted a bunch of smaller ~related issues

my plan is to address the smaller issues first and once they are resolved address the core problem - the only solution i can think of rn is to instead use the unscoped GCS cache that we use for bazel

the required changes will need to be mostly made to related toolshed actions