patch 8.2.2497: no error when using more than one character for a register

Problem:    No error when using more than one character for a register name.
Solution:   In Vim9 script check for a single character string. (closes #7814)
            Fix that VAR_BOOL and VAR_SPECIAL are not considered equal.
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index eb36bd7..cb36990 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -531,6 +531,7 @@
   var lines = ['aaa', 'bbb', 'ccc']
   setreg('a', lines)
   getreg('a', true, true)->assert_equal(lines)
+  assert_fails('getreg("ab")', 'E1162:')
 enddef
 
 def Test_getreg_return_type()
@@ -539,6 +540,20 @@
   var s3: list<string> = getreg('"', 1, 1)
 enddef
 
+def Test_getreginfo()
+  var text = 'abc'
+  setreg('a', text)
+  getreginfo('a')->assert_equal({regcontents: [text], regtype: 'v', isunnamed: false})
+  assert_fails('getreginfo("ab")', 'E1162:')
+enddef
+
+def Test_getregtype()
+  var lines = ['aaa', 'bbb', 'ccc']
+  setreg('a', lines)
+  getregtype('a')->assert_equal('V')
+  assert_fails('getregtype("ab")', 'E1162:')
+enddef
+
 def Test_glob()
   glob('runtest.vim', true, true, true)->assert_equal(['runtest.vim'])
 enddef
@@ -878,6 +893,7 @@
   var reginfo = getreginfo('a')
   setreg('a', reginfo)
   getreginfo('a')->assert_equal(reginfo)
+  assert_fails('setreg("ab", 0)', 'E1162:')
 enddef 
 
 def Test_slice()