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_cscope.vim b/src/testdir/test_cscope.vim
index f4d4208..9ffe956 100644
--- a/src/testdir/test_cscope.vim
+++ b/src/testdir/test_cscope.vim
@@ -31,9 +31,9 @@
     catch
       call assert_report('exception thrown')
     endtry
-    call assert_fails('cscope add', 'E560')
-    call assert_fails('cscope add Xcscope.out', 'E568')
-    call assert_fails('cscope add doesnotexist.out', 'E563')
+    call assert_fails('cscope add', 'E560:')
+    call assert_fails('cscope add Xcscope.out', 'E568:')
+    call assert_fails('cscope add doesnotexist.out', 'E563:')
     if has('unix')
       call assert_fails('cscope add /dev/null', 'E564:')
     endif