profile.d: Tighten the Silverblue check

The Silverblue welcome message was being displayed incorrectly on
other OSTree based OS's (Fedora Atomic Host, Fedora CoreOS, etc).

Note that none of the stable Silverblue releases that have shipped so
far (ie., until Silverblue 30) have had 'silverblue' as the VARIANT_ID.
This makes the check a bit more convoluted that it should have been.

https://github.com/debarshiray/toolbox/pull/236

profile.d/toolbox.sh

@@ -5,8 +5,13 @@ toolbox_config="$HOME/.config/toolbox"
 host_welcome_stub="$toolbox_config/host-welcome-shown"
 toolbox_welcome_stub="$toolbox_config/toolbox-welcome-shown"
 
+# shellcheck disable=SC1091
+. /usr/lib/os-release
+
 if [ -f /run/ostree-booted ] \
-   && ! [ -f "$host_welcome_stub" ]; then
+   && ! [ -f "$host_welcome_stub" ] \
+   && [ "${ID}" = "fedora" ] \
+   && { [ "${VARIANT_ID}" = "workstation" ] || [ "${VARIANT_ID}" = "silverblue" ]; }; then
     echo ""
     echo "Welcome to Fedora Silverblue. This terminal is running on the"
     echo "host system. You may want to try out the Toolbox for a directly"