ci: shellcheck: add os-installer's setup script

Signed-off-by: Clayton Craft <craftyguy@postmarketos.org>
Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/7112>

.ci/shellcheck.sh

@@ -21,6 +21,7 @@ sh_files="
 	./main/postmarketos-initramfs/init.sh
 	./main/postmarketos-initramfs/init_functions.sh
 	./main/postmarketos-mkinitfs-hook-netboot/netboot.sh
+	./main/postmarketos-ui-os-installer/rootfs-usr-bin-pmos_setup.sh
 	./main/ttyescape/*.post-install
 	./main/unl0kr/unlock.sh
 	./device/community/soc-qcom/call_audio_idle_suspend_workaround.sh