patch 9.1.0444: Not enough tests for getregion() with multibyte chars

Problem:  Not enough tests for getregion() with multibyte chars.
Solution: Add a few more tests (zeertzjq).

closes: #14844

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 866fab1..751fbc2 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -1,4 +1,4 @@
-*builtin.txt*	For Vim version 9.1.  Last change: 2024 May 24
+*builtin.txt*	For Vim version 9.1.  Last change: 2024 May 25
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -4290,7 +4290,8 @@
 
 			type		Specify the region's selection type.
 					See |getregtype()| for possible values,
-					except it cannot be an empty string.
+					except that the width can be omitted
+					and an empty string cannot be used.
 					(default: "v")
 
 			exclusive	If |TRUE|, use exclusive selection