Fix issues reported by shellcheck

Corrects the following issues currently causing spellcheck to fail.

In /home/runner/work/desktopify/desktopify/desktopify line 244:
if [ "$(env LANG=C apt list --installed ${DESKTOP_PACKAGES} 2>/dev/null | grep installed)" ] && [ "${FORCE}" -eq 0 ]; then
     ^-- SC2143: Use grep -q instead of comparing output with [ -n .. ].

In /home/runner/work/desktopify/desktopify/desktopify line 260:
apt install -y ${HARDWARE_PACKAGES}
               ^-- SC2086: Double quote to prevent globbing and word splitting.

wimpysworld / desktopify

Fix issues reported by shellcheck #41