warnings: be less picky about occurrences of m4_/b4_ in the output Reported by Marko Mäkelä. <https://lists.gnu.org/r/bug-bison/2021-10/msg00026.html> * src/scan-skel.l: It is ok to have foob4_ or foom4_. * tests/skeletons.at (Suspicious sequences): New.