[HttpKernel] Fix request _format duplication for HttpKernel's ExceptionListener

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8777
| License       | MIT

Simple fix to store the `_format` properly in a duplicated request created by the `ExceptionListener`.  See #8777.