cli: Move external git repo canonicalization into Workspace::init_g… #2830

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The following contributors were found for this pull request:

✅ 938bf01 Author: @essiene <es****e@google.com>
✅ da218d1 Author: @yuja <y**a@tcha.org>
✅ b5343fb Author: @martinvonz <mar*****nz@gmail.com>, <mar*****nz@google.com>
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