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_syntax.vim b/src/testdir/test_syntax.vim
index 96d0f1a..cd06892 100644
--- a/src/testdir/test_syntax.vim
+++ b/src/testdir/test_syntax.vim
@@ -107,7 +107,7 @@
   call assert_notmatch('.* cppNumber*', a)
   call assert_notmatch('[1-9]', a)
 
-  call assert_fails('syntime abc', 'E475')
+  call assert_fails('syntime abc', 'E475:')
 
   syntax clear
   let a = execute('syntime report')
@@ -718,8 +718,8 @@
   syntax on
   set foldmethod=syntax
 
-  call assert_fails('syn foldlevel start start', 'E390')
-  call assert_fails('syn foldlevel not_an_option', 'E390')
+  call assert_fails('syn foldlevel start start', 'E390:')
+  call assert_fails('syn foldlevel not_an_option', 'E390:')
 
   set foldlevel=1