savehist-file-modes

savehist-file-modes is a variable defined in `savehist.el'.
Its value is

384

Documentation:
Default permissions of the history file.
This is decimal, not octal. The default is 384 (0600 in octal).
Set to nil to use the default permissions that Emacs uses, typically
mandated by umask. The default is a bit more restrictive to protect
the user's privacy.

You can customize this variable.