Add Makefile to artifacts for osx_M

Author: rcedgar

.github/workflows/build_osx_M.yml

@@ -34,5 +34,6 @@ jobs:
           name: muscle-osx-m
           path: |
               /Users/runner/work/muscle/muscle/bin/muscle
+              /Users/runner/work/muscle/muscle/src/Makefile
               /Users/runner/work/muscle/muscle/src/make.stdout
               /Users/runner/work/muscle/muscle/src/make.stderr