go mod: retract

- https://github.com/caarlos0/env/commit/432567cfba936d9710fc472f7fe6b97e7ca35e23
```go
module github.com/caarlos0/env/v11

retract v11.0.1 // v11.0.1 accidentally introduced a breaking change regarding the behavior of nil pointers. You can now chose to auto-initialize them by setting the `init` tag option.

go 1.18
```