xml: Fix flags and enums

GtkBuilder XML uses enum nicknames, full names, or integer values, but
we accept GIR names, so passing those through doesn't work if the name
has an underscore (which traditionally turns into a dash in the
nickname). Avoid the problem by always writing the integer value of the
enum member.

tests/samples/accessibility.ui

@@ -5,7 +5,7 @@
     <accessibility>
       <property name="label" translatable="true">Hello, world!</property>
       <relation name="labelled-by">my_label</relation>
-      <state name="checked">true</state>
+      <state name="checked">1</state>
     </accessibility>
   </object>
   <object class="GtkLabel" id="my_label"></object>

tests/samples/enum.ui

@@ -2,6 +2,6 @@
 <interface>
   <requires lib="gtk" version="4.0"/>
   <object class="GtkScrolledWindow">
-    <property name="window-placement">top-left</property>
+    <property name="window-placement">0</property>
   </object>
 </interface>

tests/samples/flags.ui

@@ -2,9 +2,9 @@
 <interface>
   <requires lib="gtk" version="4.0"/>
   <object class="GApplication">
-    <property name="flags">is_service|handles_open</property>
+    <property name="flags">1|4</property>
   </object>
   <object class="GtkEventControllerScroll">
-    <property name="flags">vertical</property>
+    <property name="flags">1</property>
   </object>
 </interface>

tests/samples/property.ui

@@ -2,6 +2,6 @@
 <interface>
   <requires lib="gtk" version="4.0"/>
   <object class="GtkBox">
-    <property name="orientation">vertical</property>
+    <property name="orientation">1</property>
   </object>
 </interface>

tests/samples/size_group.ui

@@ -2,7 +2,7 @@
 <interface>
   <requires lib="gtk" version="4.0"/>
   <object class="GtkSizeGroup">
-    <property name="mode">horizontal</property>
+    <property name="mode">1</property>
     <widgets>
       <widget name="label"/>
       <widget name="button"/>

tests/test_samples.py

@@ -153,7 +153,7 @@ class TestSamples(unittest.TestCase):
         self.assert_sample("enum")
         self.assert_sample("expr_lookup", skip_run=True)  # TODO: Fix
         self.assert_sample("file_filter")
-        self.assert_sample("flags", skip_run=True)  # TODO: Fix
+        self.assert_sample("flags")
         self.assert_sample("id_prop")
         self.assert_sample("layout")
         self.assert_sample("menu")