patch 9.1.1405: tests: no test for mapping with special keys in session file

Problem:  tests: no test for mapping with special keys in session file.
Solution: Add a special keys to an existing test.  Also test with UTF-8
          characters containing 0x80 or 0x9b bytes (zeertzjq).

closes: #17360

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_mksession_utf8.vim b/src/testdir/test_mksession_utf8.vim
index 36cb38b..387d128 100644
--- a/src/testdir/test_mksession_utf8.vim
+++ b/src/testdir/test_mksession_utf8.vim
@@ -103,12 +103,19 @@
 endfunc
 
 func Test_session_multibyte_mappings()
-
-  " some characters readily available on european keyboards
+  " some characters readily available on european keyboards,
+  " as well as characters containing 0x80 or 0x9b bytes
   let entries = [
+        \ ['n', 'ç', 'ç'],
+        \ ['n', 'º', 'º'],
+        \ ['n', '¡', '¡'],
         \ ['n', '<M-ç>', '<M-ç>'],
         \ ['n', '<M-º>', '<M-º>'],
         \ ['n', '<M-¡>', '<M-¡>'],
+        \ ['n', '…', 'ě'],
+        \ ['n', 'ě', '…'],
+        \ ['n', '<M-…>', '<M-ě>'],
+        \ ['n', '<M-ě>', '<M-…>'],
         \ ]
   for entry in entries
     exe entry[0] .. 'map ' .. entry[1] .. ' ' .. entry[2]