`xgo mod tidy` generates `xgo_autogen.go` that is not `gofmt`-compliant

The generated `xgo_autogen.go` file requires `gofmt` to reformat it. Ideally, the output should already be properly formatted so that `gofmt` produces no changes.

This was expected to be fixed by goplus/gogen#553 (included in gogen v1.20.6, which xgo v1.6.1 depends on), but it appears the issue persists.