executable-magicless-file-regexp

executable-magicless-file-regexp is a variable defined in `executable.el'.
Its value is

"/[Mm]akefile$\\|/\\.\\(z?profile\\|bash_profile\\|z?login\\|bash_login\\|z?logout\\|bash_logout\\|.+shrc\\|esrc\\|rcrc\\|[kz]shenv\\)$"

Documentation:
On files with this kind of name no magic is inserted or changed.

You can customize this variable.