patch 9.1.0334: No test for highlight behavior with 'ambiwidth'

Problem:  No test for highlight behavior with 'ambiwidth'.
Solution: Add a screendump test for 'ambiwidth' with 'cursorline'.
          (zeertzjq)

closes: #14554

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_regexp_utf8.vim b/src/testdir/test_regexp_utf8.vim
index 6669dee..bc70544 100644
--- a/src/testdir/test_regexp_utf8.vim
+++ b/src/testdir/test_regexp_utf8.vim
@@ -342,7 +342,7 @@
 endfunc
 
 " check that 'ambiwidth' does not change the meaning of \p
-func Test_ambiwidth()
+func Test_regexp_ambiwidth()
   set regexpengine=1 ambiwidth=single
   call assert_equal(0, match("\u00EC", '\p'))
   set regexpengine=1 ambiwidth=double