pattern: only log disabling origins once

Getting this message on every page is needlessly verbose, especially in
staging where most listers are configured this way.

swh/lister/pattern.py

@@ -218,6 +218,7 @@ class Lister(Generic[StateType, PageType]):
         """
         full_stats = ListerStats()
         self.recorded_origins = set()
+        disabling_logged = False
 
         try:
             for page in self.get_pages():
@@ -237,9 +238,11 @@ class Lister(Generic[StateType, PageType]):
                         break
 
                 if not self.enable_origins:
-                    logger.info(
-                        "Disabling origins before sending them to the scheduler"
-                    )
+                    if not disabling_logged:
+                        logger.info(
+                            "Disabling origins before sending them to the scheduler"
+                        )
+                        disabling_logged = True
                     origins = [attr.evolve(origin, enabled=False) for origin in origins]
                 sent_origins = self.send_origins(origins)
                 self.recorded_origins.update(sent_origins)