Fix metadata in firewall_single_service_active rule

linux_os/guide/system/network/firewall_single_service_active/oval/shared.xml

@@ -1,13 +1,7 @@
 <def-group>
   <!-- Check that exactly one firewall service is active -->
   <definition class="compliance" id="{{{ rule_id }}}" version="1">
-    <metadata>
-      <title>Ensure Only One Firewall Service is Active</title>
-      <affected family="unix">
-        <platform>multi_platform_all</platform>
-      </affected>
-      <description>Only one firewall service (ufw, iptables, or nftables) should be active.</description>
-    </metadata>
+    {{{ oval_metadata("Ensure Only One Firewall Service is Active") }}}
     <criteria>
         <criterion comment="exactly one firewall service is active" 
             test_ref="test_{{{ rule_id }}}_single_active_firewall"/>

linux_os/guide/system/network/firewall_single_service_active/tests/multiple.fail.sh

@@ -1,4 +1,4 @@
-#!?bin/bash
+#!/bin/bash
 #
 # remediation = none
 

linux_os/guide/system/network/firewall_single_service_active/tests/none.fail.sh

@@ -1,4 +1,4 @@
-#!?bin/bash
+#!/bin/bash
 #
 # remediation = none
 

linux_os/guide/system/network/firewall_single_service_active/tests/single.pass.sh

@@ -1,4 +1,4 @@
-#!?bin/bash
+#!/bin/bash
 #
 # remediation = none