[HttpFoundation] Remove useless reflection usage in MetadataBagTest
merged branch adrienbrault/metadata-bag-test (PR #9118)

This PR was merged into the master branch.

Discussion
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[HttpFoundation] Remove useless reflection usage in MetadataBagTest

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

Commits
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ea27961 [HttpFoundation] Remove useless reflection usage in MetadataBagTest