Fix issue with file ordering

A bug exists in the logic that determines if `go.mod` exists: if a `*.go` file is returned by the filesystem before `go.mod`, we will not skip the
subtree as intended. To fix this, we always stat for `go.mod` if we find a `*.go` file, as a final check before considering the path to be
a subpackage.

pkg/config/config.go

@@ -614,7 +614,16 @@ func (c *Config) subPackages(
 				}
 			}
 
-			pathLog.Debug().Msg("subdirectory has a .go file, adding this path to packages config")
+			pathLog.Debug().Msg("subdirectory has a .go file")
+			goModExists, err := path.Parent().Join("go.mod").Exists()
+			if err != nil {
+				pathLog.Err(err).Msg("failed to determine if go.mod exists")
+				return err
+			}
+			if goModExists {
+				pathLog.Debug().Msg("found .go file, but go.mod exists. Skipping.")
+				return pathlib.ErrWalkSkipSubtree
+			}
 			subdirectoriesWithGoFiles = append(subdirectoriesWithGoFiles, path.Parent())
 			visitedDirs[path.Parent().String()] = nil
 		}