[COIL] Change chromium code search type links to use main rather than master for rlz

    See this doc: go/chromium-coil-change for more info
    BUG=1210385

Change-Id: Ibbca4dad29500690ab508f413dcaca7791a9cdb7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2902927


Auto-Submit: John Palmer <jopalmer@chromium.org>
Reviewed-by: Roger Tawa <rogerta@chromium.org>
Commit-Queue: John Palmer <jopalmer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#885301}