Move special-case LDML value to a module global

Giving it a symbolic name is clearer (and saves me the need to
duplicate the comment when I add some more references to it).
This amends commit bcdd51cfae24731a73d008add23d3c1e85bbd8d0

Pick-to: 6.5
Task-number: QTBUG-115158
Change-Id: I7577e0cde783fcda840009c7aea46934964c6e4c
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>
(cherry picked from commit 0f770b0b34bcb5fa0a598b2ff76fe215fbc25f5c)

util/locale_database/ldml.py

@@ -21,6 +21,9 @@ See individual classes for further detail.
 from localetools import Error
 from dateconverter import convert_date
 
+# The github version of CLDR uses '↑↑↑' to indicate "inherit"
+INHERIT = '↑↑↑'
+
 class Node (object):
     """Wrapper for an arbitrary DOM node.
 
@@ -205,8 +208,7 @@ class LocaleScanner (object):
                 try:
                     if draft is None or elt.draft <= draft:
                         value = elt.dom.firstChild.nodeValue
-                        # The github version of CLDR uses '↑↑↑' to indicate "inherit"
-                        if value != '↑↑↑':
+                        if value != INHERIT:
                             return value
                 except (AttributeError, KeyError):
                     pass