fix(manager/git-submodule): updates when update=none

[samgiz]

Changes

Enable updating git submodules that have update=none set in .gitmodules.

Context

When update=none, git submodule update --init doesn't pull that specific submodule. This provides a way to emulate optional dependencies that aren't vital for the repo to work, but the end user still has the option to fetch them by doing git submodule update --init --checkout for extra functionality.

Renovate would fail to successfully initialize such submodules and then fail with submodule checkout error when trying to checkout a specific commit.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[samgiz]

Here is a reproducer: https://github.com/samgiz/renovate-reproducer-32455.

[samgiz]

Is anything stopping this from being merged?