workaround checkout-error for nested shallow submodules

[ccwienk]

If a nested submodule is configured to be "shallow", referencing a commit that is not reachable from the respective repository's HEAD (typically the default branch, if e.g. hosted on GitHub), will result in an error when checking out the submodule (git submodule update..).

Workaround this by always setting --no-recommend-shallow, which lets git ignore this setting.

For a "real-world" example, see: https://github.com/google/docsy/issues/755 (I also commented there)

[xtremerui]

My knowledge with git shallow clone is limited. Would adding this flag cause users cloning more data than they want (if their submodules is meant to be shallow)?