Support Symfony 8.1 BackendEnumDenormalizer new error

[vincentchalamon]

API Platform version(s) affected: x.y.z

Description
Symfony PR #62574 (commit 35b1aec) improves BackedEnumNormalizer error messages. This change was:

1. Merged to 8.1 branch (Dec 2025)
2. Accidentally cherry-picked into 8.0.5 — which broke this demo (see PR #587 comment)
3. Reworked in 8.0.6 (commit 388c311) — the expectedTypes = null behavior was removed from 8.0.x
4. The demo jumped from v8.0.4 → v8.0.7, skipping the broken v8.0.5

On the current Symfony 8.1 branch, BackedEnumNormalizer distinguishes:

• Type mismatch (TypeError): expectedTypes = [$backingType]
• Invalid value (ValueError): expectedTypes = ['int', 'string'], message = "The data must belong to a backed enumeration of type $type"

How to reproduce
Symfony has modified its behavior for BackendEnumDenormalizer in Symfony 8.1. This change is not supported by API Platform and may cause troubles on later migration.
Reproducer: api-platform/demo#617

Possible Solution
Support both Symfony 8.0 and 8.1 behaviors.

Additional Context
PR in progress...