girnode: Make an internal struct member’s type more specific

This struct is only ever heap allocated, and enums are always the same
size as an int (or unsigned int), so it won’t change size.
The struct doesn’t correspond to any mmapped structure from a
typelib file.

This should fix some `-Wsign-conversion` warnings (curiously only seen
on the macOS CI runner) by using the most specific type.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Helps: #3405

girepository/girnode-private.h

@@ -147,7 +147,7 @@ struct _GIIrNodeType
   uint8_t is_ghashtable : 1;
   uint8_t is_interface : 1;
   uint8_t is_error : 1;
-  int tag;
+  GITypeTag tag;
 
   char *unparsed; /* (owned) */
 

girepository/girparser.c

@@ -499,7 +499,7 @@ static IntegerAliasInfo integer_aliases[] = {
 
 typedef struct {
   const char *str;
-  int tag;
+  GITypeTag tag;
   gboolean pointer;
 } BasicTypeInfo;
 

girepository/girwriter.c

@@ -221,7 +221,7 @@ write_type_info (const char *ns,
                  GITypeInfo  *info,
                  Xml         *file)
 {
-  int tag;
+  GITypeTag tag;
   GITypeInfo *type;
   gboolean is_pointer;