patch 9.1.0220: Few typos in source and test files

Problem:  Typos in code and tests.
Solution: Fix typos (zeertzjq).

closes: #14321

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 52306e8..376d82f 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -1130,7 +1130,7 @@
   edit Xfile1
   enew
   set complete=U
-  " completing from a unloaded buffer should fail
+  " completing from an unloaded buffer should fail
   exe "normal! ia\<C-X>\<C-L>\<C-P>"
   call assert_equal('a', getline(1))
   %d