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_eval_stuff.vim b/src/testdir/test_eval_stuff.vim
index 1490ffb..316fb42 100644
--- a/src/testdir/test_eval_stuff.vim
+++ b/src/testdir/test_eval_stuff.vim
@@ -35,12 +35,12 @@
   endtry
   " 'p' doesn't suppress real errors
   call writefile([], 'Xfile')
-  call assert_fails('call mkdir("Xfile", "p")', 'E739')
+  call assert_fails('call mkdir("Xfile", "p")', 'E739:')
   call delete('Xfile')
   call delete('Xmkdir', 'rf')
   call assert_equal(0, mkdir(test_null_string()))
-  call assert_fails('call mkdir([])', 'E730')
-  call assert_fails('call mkdir("abc", [], [])', 'E745')
+  call assert_fails('call mkdir([])', 'E730:')
+  call assert_fails('call mkdir("abc", [], [])', 'E745:')
 endfunc
 
 func Test_line_continuation()