Tartufo no longer able to scan repositories with GIT submodules

[adifelice-godaddy]

🐛 Bug Report

The method Repository.lookup_submodule from pygit2 was removed (deprecated). But the scanner module is still calling it causing an exception.

Line: https://github.com/godaddy/tartufo/blob/345092b4b2b237c1c940d079aedf411fdc17b383/tartufo/scanner.py#L776

To Reproduce

Scan a repository with GIT submodules.

Expected Behavior

Complete scan.

Code Example

Removing error handler exposes the actual exception:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
AttributeError: 'Repository' object has no attribute 'lookup_submodule'

Environment

Any.