Non-determinism in the go build cache test

[squaremo]

This PR introduced a test that repeated builds don't grow the go build cache (if you are building the same code at the same place, you would expect every package to be a cache hit). However, this has flaked at least once: https://github.com/pulumi/pulumi-kubernetes-operator/actions/runs/4125036191/jobs/7125062959#step:9:502

One idea: set GODEBUG=gocachehash=1 when testing the cache. I don't see any flag that just reports misses, but it might give some clues.

[squaremo]

Fixed by #416

[pulumi-bot]

Cannot close issue without required labels: kind/