fix typo

Change-Id: Ic1527cebff9c23f380e0e46f40bb002f3233f897

Author: SoloJacobs

.werks/17726.md

@@ -18,4 +18,4 @@ This behaviour has been present since its introduction, i.e., the 2.3.0b1.
 
 With this Werk, a new option 'Filter tags imported as host/service labels' is introduced.
 This Werk does not affect hosts in existing setups.
-This is because the default of the new rule always matches the behaviour of old configuration, which could be changed.
+This is because the default of the new rule always matches the behaviour of old configuration, which couldn't be changed.