Allow git_diff_find_similar() to detect renames and copies of small files

See #2735 for the background discussion.
These assertions do not tell a reader that the values need to be sequential. They only test the exact values. If someone were to change the values, they would likely simply change them here as well, as all it's testing is for the exact value. If this test want to assert them being sequential, then it must assert some property that shows they are sequential.