search: Diff search is broken for latest git CLI version

Created by: camdencheek

The latest git CLI version added a check to explicitly fail when -G and --pickaxe-regex are both specified. After upgrading git to version 2.33.0 on my dev environment, diff searches are now failing locally because the args we send to git include both of those.

Two things here:

1. we can't yet upgrade the pinned git version until it's fixed (cc @sourcegraph/distribution)
2. this will be broken for any dev who runs brew upgrade