fix(git,github): skip prepareExternalProject when enableScripts=false

[legobeat]

What's the problem this PR addresses?

It seems that the purpose of prepareExternalProject in scriptUtils.ts is to execute lifecycle scripts of fetched packages.

This disables calling the function and calling out to external package managers when the configuration enableScripts is set to false.

Related

• Resolves [Bug]: lifecycle script triggering despite enableScripts=false #6258
• Supersedes fix: propagate --ignore-scripts to yarn v1 dependency bootstrap if enableScripts=false #6259

How did you fix it?

• plugin-github: skip prepareExternalProject when configuration enableScripts is set to false
• plugin-git: skip prepareExternalProject when configuration enableScripts is set to false

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.
  • Not certain if I got this right - I put all prompted as patch

• I will check that all automated PR checks pass before the PR gets reviewed.