cmd/go: missing checksums for dependencies of `go get` arguments and tests of external dependencies [1.19 backport]

[gopherbot]

@bcmills requested issue #56222 to be considered for backport to the next 1.19 minor release.

@gopherbot, please backport to Go 1.19 and 1.20. We should at least report a clear error for missing checksums instead of trying to build with the wrong language version.

[gopherbot]

Change https://go.dev/cl/492983 mentions this issue: [release-branch.go1.19] cmd/go: save checksums for go.mod files needed for go version lines

[thanm]

The 60,000th github issue for Go-- hah! Looks like gopherbot gets to claim the prize.

[gopherbot]

Closed by merging 29f3469 to release-branch.go1.19.