The x/vulndb build has been broken on the release-branch.go1.16 builder since CL 386696 (CC @jba @julieqiu @neild). The failure was detected and reported by the TryBots (https://go-review.googlesource.com/c/vulndb/+/386696/3#message-00588b82f4f505c7202a3ccb89e76fc690afa4a7), but the CL was committed without addressing the breakage.

The policy of the Go project (documented in #11811) is that the builds for the x/ repos need to stay green, so this is a release-blocker for the Go 1.16.15 minor release (CC @golang/release).

If we don't actually care about this repo on this configuration, the builders can be configured not to run it. However, from the failure message it should also be straightforward to address by running go mod tidy -go=1.16 and committing the resulting go.sum changes.