Use actions/cache for go lint actions

[silverwind]

Attempt to use actions/cache for the go linters which in ideal case would save around 10 minutes of CI time per go lint run.

[silverwind]

Results look good. Not as much as I hoped but still a ~2 minute improvement per job:

lint-go-windows: 5m 53s -> 3m 53s
lint-go-gogit: 5m 30s -> 3m 39s
lint-backend: 10m 25s -> 7m 24s

More could be done to create another cache for deps-tools later.

[silverwind]

Now with go build cache also cached, it's quite fast. The only question is whether it is safe to cache the build cache. I assume it is but more testing will be good.

lint-go-windows: 5m 53s -> 1m 55s
lint-go-gogit: 5m 30s -> 1m 46s
lint-backend: 10m 25s -> 5m 34s

[silverwind]

Will do a bit more tweaks to always cache deps-tools content, but the current results already look very promising in terms of performance. Cache size is at 464MB, which is big, but may be acceptable, but we need to keep in mind the repo is likely limited to 10GB total cache size and those three jobs would already consume 1.4GB of that.

[silverwind]

I wonder if it's safe to retain GOCACHE between changing go versions. My intuition tells me that should be possible because that's what happens on developer machines as well, e.g. go is updated, cache remains and go correctly invalidates it.

[silverwind]

Another question in mind is whether to remove gopls lint again. It does not seem to respect any cache and always takes 3 minutes of precious CI time. golangci-lint has a seemingly working cache and I can get it down to sub 1-minute per run with cache (5 minutes with no cache).