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

* ob-scheme.el replace `geiser-eval-region` with `geiser-eval-region/wait` (only available in newer versions) 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..ffbd62bf97 100644
--- a/lisp/org/ob-scheme.el
+++ b/lisp/org/ob-scheme.el
@@ -53,8 +53,6 @@ geiser-repl-window-allow-split

 (declare-function run-geiser "ext:geiser-repl" (impl))
 (declare-function geiser-mode "ext:geiser-mode" ())
-(declare-function geiser-eval-region "ext:geiser-mode"
-                  (start end &optional and-go raw nomsg))
 (declare-function geiser-repl-exit "ext:geiser-repl" (&optional arg))
 (declare-function geiser-eval--retort-output "ext:geiser-eval" (ret))
 (declare-function geiser-eval--retort-result-str "ext:geiser-eval" (ret prefix))
@@ -176,7 +174,14 @@ 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 (funcall
+			;; use `geiser-eval-region/wait' only when available
+			;; in newer versions of `geiser'
+			(if (fboundp 'geiser-eval-region/wait)
+			    'geiser-eval-region/wait
+			  'geiser-eval-region)
+			(point-min)
+			(point-max))))
 	      (setq result (if output
 			       (or (geiser-eval--retort-output ret)
 				   "Geiser Interpreter produced no output")