Log stack traces for OldDataMonitor.report on Run (#27500)

* Log stack straces for `OldDataMonitor.report` on `Run`

* Ignore `ReportException` https://github.com/jenkinsci/jenkins/pull/27500#discussion_r4195992415

* Reduce messages to `FINE` so they can be collected if and when desired https://github.com/jenkinsci/jenkins/pull/27500#discussion_r4196269765

core/src/main/java/hudson/diagnosis/OldDataMonitor.java

@@ -185,6 +185,11 @@ public class OldDataMonitor extends AdministrativeMonitor {
      */
     public static void report(Saveable obj, Collection<Throwable> errors) {
         if (obj instanceof Run<?, ?>) {
+            if (LOGGER.isLoggable(Level.FINE)) {
+                for (var error : errors) {
+                    LOGGER.log(Level.FINE, "Trouble loading " + obj, error);
+                }
+            }
             return; // somewhat ephemeral
         }
         StringBuilder buf = new StringBuilder();