gitserver: Handle and ignore filepath.Walk error

Created by: keegancsmith

filepath.Walk can return errors if we run into permission errors or a file disappears between readdir and the stat of the file. In either case this error isn't important for our cleanup, so we just ignore it. This is what we typically do in the rest of the gitserver uses of filepath.Walk

Previously we ignored the error completely, which would lead to info being nil => panic. This bug has existed for a long time, but is a hard to trip panic.

Fixes https://github.com/sourcegraph/sourcegraph/issues/6710

Created by: codecov[bot]

Codecov Report

Merging #7030 into master will increase coverage by <.01%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #7030      +/-   ##
==========================================
+ Coverage   39.23%   39.23%   +<.01%     
==========================================
  Files        1230     1230              
  Lines       63533    63535       +2     
  Branches     6041     6041              
==========================================
+ Hits        24924    24926       +2     
  Misses      36326    36326              
  Partials     2283     2283

Impacted Files	Coverage Δ
cmd/gitserver/server/cleanup.go	64.18% <0%> (-0.37%)
cmd/frontend/graphqlbackend/repository.go	21.65% <0%> (+0.92%)

Created by: keegancsmith

Might be worth adding a bit more context to the comment.

I'll follow-up with a clearer API to be used across gitserver.

Created by: keegancsmith

Might be worth adding a bit more context to the comment.

I'll follow-up with a clearer API to be used across gitserver.

!7032 (merged)