FIX Resilient log handler implementation

The log handler on QueuedJobService is triggering a write to the database on log messages.
It's added to the *global logger singleton*, meaning it applies beyond the scope of this service execution.
That's problematic when completely unrelated logic writes new log messages,
and the buffer flushes - at the latest point, during PHP shutdown.
At this point, a database is often no longer in a state to accept the write,
e.g. during unit test execution.

Note that a better fix would be to use a specific logger instance clone
for this purpose, but we do want to inherit the log handlers set up for a specific project here,
so can't just create a logger from scratch.

src/Services/QueuedJobService.php

@@ -882,11 +882,6 @@ public function runJob($jobId)
                             $this->extend('updateJobDescriptorAndJobOnException', $jobDescriptor, $job, $e);
                         }
 
-                        // Write any remaining batched messages at the end
-                        if (isset($bufferHandler)) {
-                            $bufferHandler->flush();
-                        }
-
                         ob_end_flush();
 
                         // now check the job state
@@ -964,6 +959,24 @@ public function runJob($jobId)
                 $this->handleBrokenJobException($jobDescriptor, $job, $e);
                 $broken = true;
             }
+
+            // Write any remaining batched messages at the end.
+            if ($logger instanceof Logger) {
+                foreach ($logger->getHandlers() as $handler) {
+                    if ($handler instanceof BufferHandler) {
+                        $handler->flush();
+                    }
+                }
+            }
+
+            // If using a global singleton logger here,
+            // any messages added after this point will be auto-flushed on PHP shutdown through the handler.
+            // This causes a database write, and assumes the database and table will be available at this point.
+            if ($logger instanceof Logger) {
+                $logger->setHandlers(array_filter($logger->getHandlers(), function ($handler) {
+                    return !($handler instanceof BufferHandler);
+                }));
+            }
         });
 
         $this->unsetRunAsUser($runAsUser, $originalUser);