Stop logging CheckPath returns error: context canceled (#21064)

We should only log CheckPath errors if they are not simply due to
context cancellation - and we should add a little more context to the
error message.

Fix #20709

Signed-off-by: Andrew Thornton <art27@cantab.net>

services/gitdiff/gitdiff.go

@@ -1178,8 +1178,6 @@ func GetDiff(gitRepo *git.Repository, opts *DiffOptions, files ...string) (*Diff
 				} else if language, has := attrs["gitlab-language"]; has && language != "unspecified" && language != "" {
 					diffFile.Language = language
 				}
-			} else {
-				log.Error("Unexpected error: %v", err)
 			}
 		}