doc: correct typo (#21176)

Changed files
+1 -1
nixos
+1 -1
nixos/doc/manual/man-nixos-rebuild.xml
···
<listitem>
<para>Build and activate the new configuration, and make it the
boot default. That is, the configuration is added to the GRUB
-
boot menu as the default meny entry, so that subsequent reboots
+
boot menu as the default menu entry, so that subsequent reboots
will boot the system into the new configuration. Previous
configurations activated with <command>nixos-rebuild
switch</command> or <command>nixos-rebuild boot</command> remain