nixos/installer: Mark scripts as Bash for ShellCheck

See <https://github.com/koalaman/shellcheck/wiki/SC2239>.

Changed files
+4
nixos
modules
+1
nixos/modules/installer/tools/nixos-build-vms/nixos-build-vms.sh
···
#! @runtimeShell@ -e
+
# shellcheck shell=bash
# Shows the usage of this command to the user
+1
nixos/modules/installer/tools/nixos-enter.sh
···
#! @runtimeShell@
+
# shellcheck shell=bash
set -e
+1
nixos/modules/installer/tools/nixos-install.sh
···
#! @runtimeShell@
+
# shellcheck shell=bash
set -e
shopt -s nullglob
+1
nixos/modules/installer/tools/nixos-version.sh
···
#! @runtimeShell@
+
# shellcheck shell=bash
case "$1" in
-h|--help)