Actually determine if we are dealing with a shallow clone instead of …

[tarkatronic]

…assuming

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• Tests (if applicable)
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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Tests
• Other

Backward Compatibility

Is this change backward compatible with the most recently released version? Does it introduce changes which might change the user experience in any way? Does it alter the API in any way?

• Yes (backward compatible)
• No (breaking changes)

Issue Linking

What's new?

Previously we checked to see if there were any local branches/refs to see if the clone was shallow. That worked great in PRs, because they have no local refs. Unfortunately when tartufo was used to scan against a branch that was a shallow clone, it failed again.

Now, we use a slightly more reliable method. When a shallow clone is created, a .git/shallow file is created. So now we check for that instead. This should work both in the case of a PR and in the case of a branch scan.