codeintel: make worker not depend on global repo store

Created by: slimsag

Before this PR, the worker handler - requeueIfCloning - would depend on the global backend.Repos store. This is deprecated in favor of passing stores around to where they are appropriate.

I intend to use the repo store elsewhere, so cleaning this up seems appropriate.

Helps #21938

Signed-off-by: Stephen Gutekanst stephen@sourcegraph.com