1.12.1 has inconsistent vendored Go modules

[stblassitude]

• Gitea version (or commit ref): 1.12.1
• Git version:
• Operating system: FreeBSD
• Database (use [x]): n/a
• Can you reproduce the bug at https://try.gitea.io: n/a

Description

Trying to update the FreeBSD port (==package build) to 1.12.1. Running gmake produces the following output:

gmake[2]: Entering directory '/var/ports/work/usr/home/vagrant/gitea/work/gitea-1.12.1'
go: inconsistent vendoring in /var/ports/work/usr/home/vagrant/gitea/work/gitea-1.12.1:
	src.techknowlogick.com/xgo@v0.0.0-20200602060627-a09175ea9056: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt

run 'go mod vendor' to sync, or use -mod=mod or -mod=readonly to ignore the vendor directory
CC= GOOS= GOARCH= go generate -mod=vendor -tags 'pam sqlite sqlite_unlock_notify' 
go: inconsistent vendoring in /var/ports/work/usr/home/vagrant/gitea/work/gitea-1.12.1:
	src.techknowlogick.com/xgo@v0.0.0-20200602060627-a09175ea9056: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt

run 'go mod vendor' to sync, or use -mod=mod or -mod=readonly to ignore the vendor directory
gmake[2]: *** [Makefile:518: generate] Error 1

This is from the release archive hosted at https://github.com/go-gitea/gitea/releases/download/v1.12.1/gitea-src-1.12.1.tar.gz

Running gmake vendor and restarting the build makes the build succeed.

[techknowlogick]

Closed with #12030