patch 9.1.1325: tests: not checking error numbers properly

Problem:  tests: not checking error numbers properly.
Solution: Add a trailing comma to avoid matching a different error
          number with the same prefix (zeertzjq)

closes: #17159

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_edit.vim b/src/testdir/test_edit.vim
index dbeb78d..b925b23 100644
--- a/src/testdir/test_edit.vim
+++ b/src/testdir/test_edit.vim
@@ -2083,7 +2083,7 @@
 func Test_read_invalid()
   set encoding=latin1
   " This was not properly checking for going past the end.
-  call assert_fails('r`=', 'E484')
+  call assert_fails('r`=', 'E484:')
   set encoding=utf-8
 endfunc