patch 8.2.1593: tests do not check the error number properly

Problem:    Tests do not check the error number properly.0
Solution:   Add a colon after the error number. (closes #6869)
diff --git a/src/testdir/test_rename.vim b/src/testdir/test_rename.vim
index 664a247..53fa3ff 100644
--- a/src/testdir/test_rename.vim
+++ b/src/testdir/test_rename.vim
@@ -113,8 +113,8 @@
   " Can't rename to en empty file name.
   call assert_notequal(0, rename('Xrenamefile', ''))
 
-  call assert_fails('call rename("Xrenamefile", [])', 'E730')
-  call assert_fails('call rename(0z, "Xrenamefile")', 'E976')
+  call assert_fails('call rename("Xrenamefile", [])', 'E730:')
+  call assert_fails('call rename(0z, "Xrenamefile")', 'E976:')
 
   call delete('Xrenamefile')
 endfunc