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_textprop.vim b/src/testdir/test_textprop.vim
index bacb288..012b3eb 100644
--- a/src/testdir/test_textprop.vim
+++ b/src/testdir/test_textprop.vim
@@ -314,8 +314,8 @@
   unlet props[3]
   call assert_equal(props, prop_list(1))
 
-  call assert_fails("call prop_remove({'id': 11, 'both': 1})", 'E860')
-  call assert_fails("call prop_remove({'type': 'three', 'both': 1})", 'E860')
+  call assert_fails("call prop_remove({'id': 11, 'both': 1})", 'E860:')
+  call assert_fails("call prop_remove({'type': 'three', 'both': 1})", 'E860:')
 
   call DeletePropTypes()
   bwipe!