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_writefile.vim b/src/testdir/test_writefile.vim
index a1cf686..c858b75 100644
--- a/src/testdir/test_writefile.vim
+++ b/src/testdir/test_writefile.vim
@@ -310,7 +310,7 @@
     autocmd BufWritePre Xfile enew | write
   augroup END
   e Xfile
-  call assert_fails('lockmarks write', ['E32', 'E203:'])
+  call assert_fails('lockmarks write', ['E32:', 'E203:'])
   augroup WriteTest
     au!
   augroup END