repo-updater: Fix syncRepo logic

Created by: ryanslade

syncRepo syncs a single repo that has been sourced from a single code host. It is usually triggered by lazy syncing. Since it is only sourced from a single code host its Sources map only contained mapping for that one source. Our diff algorithm thus triggered the removal of the repo from all other sources in the external_service_repos table.

Instead, we now assume that the current stored mapping is correct for all OTHER sources.

Closes: https://github.com/sourcegraph/sourcegraph/issues/15820

Created by: tsenart

Some failing lints.

Created by: codecov[bot]

Codecov Report

Merging #16176 (1bd7f4b) into main (954acf2) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main   #16176   +/-   ##
=======================================
  Coverage   52.76%   52.77%           
=======================================
  Files        1646     1646           
  Lines       82292    82296    +4     
  Branches     7285     7285           
=======================================
+ Hits        43423    43432    +9     
+ Misses      35016    35013    -3     
+ Partials     3853     3851    -2     

Flag	Coverage Δ		*Carryforward flag
go	52.55% <100.00%> (+0.01%)
integration	28.43% <ø> (ø)		Carriedforward from 4763420
storybook	28.03% <ø> (ø)		Carriedforward from 4763420
typescript	53.30% <ø> (ø)		Carriedforward from 4763420
unit	35.88% <ø> (ø)		Carriedforward from 4763420

*This pull request uses carry forward flags. Click here to find out more.

Impacted Files	Coverage Δ
cmd/repo-updater/repos/syncer.go	77.16% <100.00%> (+0.77%)
cmd/repo-updater/repos/types.go	69.37% <0.00%> (+0.62%)
.../internal/codeintel/resolvers/graphql/locations.go	85.56% <0.00%> (+2.06%)