Avoid substitution issue in kustomize credentials sync

Signed-off-by: Tim Jacomb <tim.jacomb@hmcts.net>

manifests/integrations/registry-credentials-sync/_cronjobs/_base/sync.yaml

@@ -48,10 +48,10 @@ spec:
               $(RECONCILE_SH)
 
               apply-secret() {
-                /kbin/kubectl create secret docker-registry "${1}" \
-                  --docker-password="${2}" \
-                  --docker-username="${3}" \
-                  --docker-server="${4}" \
+                /kbin/kubectl create secret docker-registry "$1" \
+                  --docker-password="$2" \
+                  --docker-username="$3" \
+                  --docker-server="$4" \
                   --dry-run=client -o=yaml \
                   | grep -v "creationTimestamp:" \
                   | /kbin/kubectl apply -f -