main/postmarketos-mkinitfs-hook-ci: Handle shellcheck checks

- Point shellcheck to the files this is sourcing
 - Tell it about the shell in use
 - Drop unused variable (grepped around)

The last change is about how the hooks are ran. The warning shellcheck
was giving was that using `if <command...>; then ...; fi` is preferred,
instead of comparing `$?`.

This is exactly what is now being done, so the branches have been
swapped around, and the command (full path to a hook) is being used
within the if condition.

Signed-off-by: Samuel Dionne-Riel <samuel@dionne-riel.com>
Part-of: https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/6335

main/postmarketos-mkinitfs-hook-ci/05-ci.sh

@@ -1,9 +1,10 @@
 #!/bin/sh
-# shellcheck disable=SC1091
-. ./init_functions.sh
-. /usr/share/misc/source_deviceinfo
+# shellcheck shell=busybox
 
-TEST=""
+# shellcheck source=../postmarketos-initramfs/init_functions.sh
+. ./init_functions.sh
+# shellcheck source=../devicepkg-utils/source_deviceinfo
+. /usr/share/misc/source_deviceinfo
 
 DID_FAIL=0
 
@@ -12,13 +13,12 @@ echo "==> disabling dmesg on console"
 dmesg -n 2
 
 for f in /usr/libexec/pmos-tests-initramfs/*; do
-	echo -e "\n==> Running test $f\n\n"
-	$f
-	if [ $? -ne 0 ]; then
+	printf '\n==> Running test "%s"\n\n\n' "$f"
+	if $f; then
+		echo "==> OK: $f"
+	else
 		echo "==> FAIL: $f"
 		DID_FAIL=1
-	else
-		echo "==> OK: $f"
 	fi
 done