internal/worker: replace fetchAndInsertModule with FetchAndUpdateState in tests
internal/worker: replace fetchAndInsertModule with FetchAndUpdateState in tests

fetchAndInsertModule is a private function and implementation detail of
internal/worker. FetchAndUpdateState is used instead for relevant tests.

Change-Id: I39dac1e6272a67248e7adb2b3c540c418f99ba72
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/729862
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite