CI: shellcheck: ignore SC3043 (MR 12)

Ignore the error for "In POSIX sh, local is undefined". Like in Alpine's
source code for abuild, we rather use local here and avoid related
mistakes even if it is not POSIX. The busybox sh supports it.

Add the ignore to .ci/shellcheck.sh and remove individual ignore lines
from upgrade.sh.

Related: https://www.shellcheck.net/wiki/SC3043

.ci/shellcheck.sh

@@ -21,5 +21,5 @@ sh_files="
 for file in $sh_files; do
 	echo "Test with shellcheck: $file"
 	cd "$DIR/$(dirname "$file")"
-	shellcheck -e SC1008 -x "$(basename "$file")"
+	shellcheck -e SC1008,SC3043 -x "$(basename "$file")"
 done

upgrade.sh

@@ -145,7 +145,7 @@ check_is_pmos() {
 }
 
 get_channel_current() {
-	# shellcheck disable=SC2155,SC3043
+	# shellcheck disable=SC2155
 	local ret="$(grep '^VERSION="' /etc/os-release  | cut -d '"' -f 2)"
 	case "$ret" in
 		v*)
@@ -236,9 +236,7 @@ get_mirrordir_pmos() {
 }
 
 get_mirrordir_alpine() {
-	# shellcheck disable=SC3043
 	local channel="$1"
-	# shellcheck disable=SC3043
 	local i
 
 	for i in $CHANNELS_ALL; do
@@ -326,9 +324,7 @@ check_upgrade_script_changed() {
 }
 
 replace_apk_repositories () {
-	# shellcheck disable=SC3043
 	local old="$VAR_LIB_DIR/etc-apk-repositories.old"
-	# shellcheck disable=SC3043
 	local new="$VAR_LIB_DIR/etc-apk-repositories.new"
 
 	cp /etc/apk/repositories "$old"
@@ -380,7 +376,7 @@ step_upgrade_packages_new_dry_run() {
 }
 
 verify_channel_after_upgrade() {
-	# shellcheck disable=SC2155,SC3043
+	# shellcheck disable=SC2155
 	local channel_after_upgrade="$(get_channel_current)"
 
 	msg "Verifying channel in /etc/os-release..."