spec: Fix test for rendering default Git binary path

What does this MR do?

When we've introduced a default Git binary path in b157bbe5 (gitaly: enable bundled git as default and set a default binary, 2022-02-18), we also added a spec which asserts that we write the expected default Git binary path. But this spec doesn't make a lot of sense: we assert that we don't write the default path if unset, which only passed because we were accidentally missing the quotation marks. Instead, we should be asserting that the default path is written as expected.

Fix the spec to do so.

Checklist

See Definition of done.

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Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for the GitLab Chart opened