[Security] fixed a leak in the ContextListener
[Security] fixed a leak in ExceptionListener
merged branch fabpot/firewall-leaks (PR #8946)

This PR was merged into the 2.2 branch.

Discussion
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[Security] fixed a leak in the ContextListener

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Trying to fix leaks when using the same Kernel to handle several requests in a row without resetting the Container or shutting down the Kernel.

Commits
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899f176 [Security] fixed a leak in ExceptionListener
2fd8a7a [Security] fixed a leak in the ContextListener