Use semerr

Co-authored-by: Maksym Kryvchun <hedhyw@yahoo.com>

internal/pkg/source/source.go

@@ -116,7 +116,7 @@ func (is *Source) CanFollow() bool {
 	return len(is.name) != 0
 }
 
-var ErrFileTruncated = errors.New("file truncated")
+const ErrFileTruncated semerr.Error = "file truncated"
 
 // ReadLogEntry reads the next ReadLogEntry from the file.
 func (is *Source) ReadLogEntry() (LazyLogEntry, error) {