fix lint errors, enable CI

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

cmd/dagger-frontend/main.go

@@ -1,14 +0,0 @@
-package main
-
-import (
-	"dagger.cloud/go/dagger"
-	"github.com/moby/buildkit/frontend/gateway/grpcclient"
-	"github.com/moby/buildkit/util/appcontext"
-)
-
-func main() {
-	r := &dagger.Runtime{}
-	if err := grpcclient.RunFromEnvironment(appcontext.Context(), r.BKFrontend); err != nil {
-		panic(err)
-	}
-}