fix: provide path to go.sum for caching

[HastD]

This prevents warnings about a missing dependency file.

[ianlewis]

The reason we haven't done this in the past was so that we could avoid issues with cache poisoning. We never really had time to address the issue intelligently.

[HastD]

@ianlewis In that case, would it be better to pass cache: false to actions/setup-go to disable caching for now? I think one or the other—either disabling caching or fixing the dependency file path—should be done, because currently the warnings about a missing dependency file are getting propagated into GitHub actions annotations for anything that uses this action. (You can see an example of this here.)

[HastD]

@ianlewis Just following up on this—should I go ahead and change this PR to set cache: false to disable caching?