dev/sg: do not fail on new 'log15.' reference

Created by: bobheadxi

This is too sensitive to code moves right now like https://github.com/sourcegraph/sourcegraph/pull/34954/files#diff-25af0d5a05b8cfbaa77a680629d8e02b3d5f1ae6c8595c81448e8d97846718e3R120 . We could maybe deduplicate the added/removed diff if the line is the same after whitespace removal but for now we just loosen the check.

Test plan

n/a