When we're running on a git checkout of WebKit, the WPT exporter just gets its patch from `git diff`. This includes blob IDs, which means we can then use `git apply --3way` when applying the patch to the WPT tree, which has a better chance of succeeding (unless the file got modified during import) as the blob the patch applies to is recorded and therefore git doesn't just blindly try to apply it to the tip-of-tree of WPT, but can use its merge machinery.