tstest/staticcheck: import the main package to fix "go mod tidy"

Importing the non-main package was missing some dependencies that
"go mod tidy" would then cleanup. Also added a non-ignore build tag to
avoid other tools getting upset about importing a main package.

Signed-off-by: Filippo Valsorda <hi@filippo.io>

go.sum

@@ -19,6 +19,7 @@ github.com/Azure/go-autorest/autorest/mocks v0.1.0/go.mod h1:OTyCOPRA2IgIlWxVYxB
 github.com/Azure/go-autorest/autorest/mocks v0.2.0/go.mod h1:OTyCOPRA2IgIlWxVYxBee2F5Gr4kF2zd2J5cFRaIDN0=
 github.com/Azure/go-autorest/logger v0.1.0/go.mod h1:oExouG+K6PryycPJfVSxi/koC6LSNgds39diKLz7Vrc=
 github.com/Azure/go-autorest/tracing v0.5.0/go.mod h1:r/s2XiOKccPW3HrqB+W0TQzfbtp2fGCgRFtBroKn4Dk=
+github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
 github.com/Masterminds/semver/v3 v3.0.3 h1:znjIyLfpXEDQjOIEWh+ehwpTU14UzUPub3c3sm36u14=

tstest/staticcheck/staticcheck.go

@@ -5,8 +5,10 @@
 // This file exists just so go mod tidy won't remove
 // staticcheck's module from our go.mod.
 
+// +build tools
+
 package tstest
 
 import (
-	_ "honnef.co/go/tools/staticcheck"
+	_ "honnef.co/go/tools/cmd/staticcheck"
 )