Fix ".bin" not linked when preparing a git dependency

[Volune]

Summary

Fix installation issue reported by @sammarks in #3553

• I have package-a that depends on package-b (through a git URL as package-b is not published to a registry).
• package-a and package-b both use Babel (listed in devDependencies in both).
• package-b's prepare script is: babel --optional runtime src -d dist

When installing the dependencies of package-a, I get an error message: babel: command not found

Test plan

Improved test in __test__/fetchers.js (Updated test dependency Volune/test-js-git-repo@1958040 and Volune/test-js-git-repo@c455e0c)