chore(codeowners): add codeowners for calendar and contacts impl

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>

Author: kesselb

.github/CODEOWNERS

@@ -95,6 +95,8 @@ ResponseDefinitions.php             @provokateurin @nextcloud/server-backend
 # Groupware
 /build/integration/dav_features/caldav.feature   @st3iny @SebastianKrupinski @tcitworld
 /build/integration/dav_features/carddav.feature  @hamza221 @SebastianKrupinski
+/lib/private/Calendar                            @st3iny @SebastianKrupinski @tcitworld
+/lib/private/Contacts                            @hamza221 @SebastianKrupinski
 /lib/public/Calendar                             @st3iny @SebastianKrupinski @tcitworld
 /lib/public/Contacts                             @hamza221 @SebastianKrupinski