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_hlsearch.vim b/src/testdir/test_hlsearch.vim
index 58e1d8c..db54ed4 100644
--- a/src/testdir/test_hlsearch.vim
+++ b/src/testdir/test_hlsearch.vim
@@ -28,7 +28,7 @@
   set nohls
   exe "normal! /\<CR>" | redraw
   call assert_notequal(r1, screenattr(1,1))
-  call assert_fails('let v:hlsearch=[]', 'E745')
+  call assert_fails('let v:hlsearch=[]', 'E745:')
   call garbagecollect(1)
   call getchar(1)
   enew!