inwx: Be case insensitive while searching for the cookie.

At least since 2023-08-25 the cookie is set via `set-cookie' instead the
expecting `Set-Cookie' string. A month earlier it was working.

Ignore the case while matching the cookie.

Fixes: #4763
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

dnsapi/dns_inwx.sh

@@ -194,7 +194,7 @@ _inwx_login() {
 
   response="$(_post "$xml_content" "$INWX_Api" "" "POST")"
 
-  INWX_Cookie=$(printf "Cookie: %s" "$(grep "domrobot=" "$HTTP_HEADER" | grep "^Set-Cookie:" | _tail_n 1 | _egrep_o 'domrobot=[^;]*;' | tr -d ';')")
+  INWX_Cookie=$(printf "Cookie: %s" "$(grep "domrobot=" "$HTTP_HEADER" | grep -i "^Set-Cookie:" | _tail_n 1 | _egrep_o 'domrobot=[^;]*;' | tr -d ';')")
   _H1=$INWX_Cookie
   export _H1
   export INWX_Cookie