[CI] Fix CI setup to not reuse a cache if the destination branch changes on a PR

[jferrant]

Describe the bug
Currently CI avoids fully re-running based on commit sha to enable build reuse. However, this does not account for destination branches changing. So if you open a PR against branch A and it builds, but then you change to against branch B, it will reuse the archive as it has the same commit hash. However, it should rebuild and fully rerun in this scenario. Update it to do so.

[wileyj]

ohhh interesting. i see how you ran into this - it's not something i had considered.

for now, the band-aid fix is to delete any cache in the github actions UI manually an re-run a workflow.

i think this may be easier to resolve than i anticipated by simply changing the cache-key to include the target(?) branch in the name

[wileyj]

#4168