[fix] Apply black formatting to VpnClient deletion code openwisp#1221

Fixes openwisp#1221

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mn-ram

openwisp_controller/config/base/config.py

@@ -352,8 +352,7 @@ def manage_vpn_clients(cls, action, instance, pk_set, **kwargs):
                             vpnclient.delete()
                     except Exception:
                         logger.exception(
-                            "Failed to delete VpnClient (id: %s) "
-                            "for Config %s",
+                            "Failed to delete VpnClient (id: %s) " "for Config %s",
                             vpnclient.pk,
                             instance,
                         )
@@ -406,8 +405,7 @@ def manage_vpn_clients(cls, action, instance, pk_set, **kwargs):
                         vpnclient.delete()
                 except Exception:
                     logger.exception(
-                        "Failed to delete VpnClient (id: %s) "
-                        "for Config %s",
+                        "Failed to delete VpnClient (id: %s) " "for Config %s",
                         vpnclient.pk,
                         instance,
                     )