Support Go 1.17 compiler toolchain

[gmlewis]

In #1889, a simple typo fix in the README.md file demonstrated that the Go 1.17 compiler toolchain is now modifying the formatting of // +build lines.

We will need to fix this before we are able to continue merging PRs.

[gmlewis]

https://tip.golang.org/doc/go1.17
https://go.googlesource.com/proposal/+/master/design/draft-gobuild.md

[willnorris]

Should be as simple as adding the new syntax. From https://tip.golang.org/doc/go1.17:

As of this release, the new syntax is fully supported, and all Go files should be updated to have both forms with the same meaning.

[willnorris]

Though I'm very surprised that actions/setup-go is included a beta release for the "1.x" go version. I would expect that to be the latest stable release. I seem to recall running into this before, so will look into that separately.

[willnorris]

fixed the "1.x" stable release issue in 77dd0eb