feat(submodules): use env vars from getGitEnvironmentVariables

[tim-thacker-nullify]

Changes

This change uses the existing getGitEnvironmentVariables function during the cloning of git submodules.

This function has been used to include support for updating private git ssh submodules on github.com, but it was not added in the function triggered when the cloneSubmodules config file option is set to true.

see: #22061

Context

#30942

Private submodules on the github.com app cannot currently be cloned with the cloneSubmodules option when the .gitmodules file is configured with ssh.

This is because the GitHub App token does not have SSH permissions, it can only auth via HTTP.

My use case is private Go submodules on github.com, for the "postUpdateOptions": ["gomodTidy", "gomodUpdateImportPaths"], options to work, I need my private git submodules cloned.

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

[rarkins]

Was git already passing all env variables before this? Because normally we'd want this controlled by exposeAllEnv.