docs/variant-format: Clarify h type string

It was confusing that int32 was mentioned twice.

docs/reference/glib/gvariant-format-strings.md

@@ -73,7 +73,7 @@ The equivalent C types are as follows:
 | `u`       | `guint32`         |
 | `x`       | `gint64`          |
 | `t`       | `guint64`         |
-| `h`       | `gint32`          |
+| `h`       | `gint32` (handle) |
 | `d`       | `gdouble`         |
 
 Note that in C, small integer types in variable argument lists are promoted