[JENKINS-75602] Report URL in update center failure messages

core/src/main/java/hudson/PluginManager.java

@@ -2177,13 +2177,15 @@
             FormValidation v = site.updateDirectlyNow();
             if (v.kind != FormValidation.Kind.OK) {
                 // Stop with an error
+                LOGGER.log(Level.SEVERE, "Failed to check updates server:  " + site.getUrl());
                 return v;
             }
         }
         for (DownloadService.Downloadable d : DownloadService.Downloadable.all()) {
             FormValidation v = d.updateNow();
             if (v.kind != FormValidation.Kind.OK) {
                 // Stop with an error
+                LOGGER.log(Level.SEVERE, "Failed to update downloadable: " + d.getUrl());
                 return v;
             }
         }