Jobs in the WorkflowJob class can't be modified.

## Installed Version
`1.47`

## Step
Manage Jenkins -> Configuration Slicing -> `Discard Old Builds Slicer - Max # of builds to keep`

## Symptom
- Jobs of the `WorkflowJob` class are not visible on the screen.
   So, Jobs in the `WorkflowJob` class can't be modified.

## Class Name
`org.jenkinsci.plugins.workflow.job.WorkflowJob`



