Fix FileNotFoundError invocation in Git SCMTool
Fix FileNotFoundError invocation in Git SCMTool

The Git SCMTool was providing the commit SHA to the `FileNotFoundError`,
leading to misleading error messages. This has been fixed.

Testing Done:
Triggered a `FileNotFoundError` in a Git repository and saw the correct
error message.

Reviewed at https://reviews.reviewboard.org/r/9901/

reviewboard/reviewboard,chipx86/reviewboard,chipx86/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,reviewboard/reviewboard