docs: Add missing language annotations

gio/gdbusauthobserver.c

@@ -45,7 +45,7 @@
  * processes owned by the same uid as the server, you would use a
  * signal handler like the following:
  * 
- * |[
+ * |[<!-- language="C" -->
  * static gboolean
  * on_authorize_authenticated_peer (GDBusAuthObserver *observer,
  *                                  GIOStream         *stream,

glib/ghash.c

@@ -810,7 +810,7 @@ iter_remove_or_steal (RealIter *ri, gboolean notify)
  * values are freed yourself.
  *
  * It is safe to continue iterating the #GHashTable afterward:
- * |[
+ * |[<!-- language="C" -->
  * while (g_hash_table_iter_next (&iter, &key, &value))
  *   {
  *     if (condition)

glib/gvariant.c

@@ -3665,7 +3665,7 @@ g_variant_builder_end (GVariantBuilder *builder)
  *
  * ## Using a stack-allocated GVariantDict
  *
- * |[
+ * |[<!-- language="C" -->
  *   GVariant *
  *   add_to_count (GVariant  *orig,
  *                 GError   **error)
@@ -3689,7 +3689,7 @@ g_variant_builder_end (GVariantBuilder *builder)
  *
  * ## Using heap-allocated GVariantDict
  *
- * |[
+ * |[<!-- language="C" -->
  *   GVariant *
  *   add_to_count (GVariant  *orig,
  *                 GError   **error)
@@ -5158,7 +5158,7 @@ g_variant_valist_get (const gchar **str,
  * specified in @format_string. This can be achieved by casting them. See
  * the [GVariant varargs documentation][gvariant-varargs].
  *
- * |[
+ * |[<!-- language="C" -->
  * MyFlags some_flags = FLAG_ONE | FLAG_TWO;
  * const gchar *some_strings[] = { "a", "b", "c", NULL };
  * GVariant *new_variant;