update to new API call to evaluate region and wait for result

* ob-scheme.el replace `geiser-eval-region` with `geiser-eval-region/wait` as the former changed expected behaviour; the latter returns the result of evaluating.

diff --git a/lisp/org/ob-scheme.el b/lisp/org/ob-scheme.el
index f4836b23fe..89c6abf686 100644
--- a/lisp/org/ob-scheme.el
+++ b/lisp/org/ob-scheme.el
@@ -176,7 +176,7 @@ org-babel-scheme-execute-with-geiser
 	  (setq geiser-impl--implementation nil)
 	  (let ((geiser-debug-jump-to-debug-p nil)
 		(geiser-debug-show-debug-p nil))
-	    (let ((ret (geiser-eval-region (point-min) (point-max))))
+	    (let ((ret (geiser-eval-region/wait (point-min) (point-max))))
 	      (setq result (if output
 			       (or (geiser-eval--retort-output ret)
 				   "Geiser Interpreter produced no output")