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_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 8ebcc28..ed7648e 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -1575,8 +1575,8 @@
   CheckScriptFailure(['vim9script', 'let str: string', 'str = 1234'], 'E1012:')
   CheckScriptFailure(['vim9script', 'const str = "asdf"', 'str = "xxx"'], 'E46:')
 
-  assert_fails('vim9script', 'E1038')
-  assert_fails('export something', 'E1043')
+  assert_fails('vim9script', 'E1038:')
+  assert_fails('export something', 'E1043:')
 enddef
 
 func Test_import_fails_without_script()