Its an enabled-by-default deprecation warning
=item do "%s" failed, '.' is no longer in @INC; did you mean do "./%s"?
-(W deprecated) Previously C< do "somefile"; > would search the current
+(D deprecated) Previously C< do "somefile"; > would search the current
directory for the specified file. Since perl v5.26.0, F<.> has been
removed from C<@INC> by default, so this is no longer true. To search the
current directory (and only the current directory) you can write