Add tests for RequestStack class
minor #10326 [HttpFoundation][Tests] Add tests for RequestStack class (inalgnu)

This PR was submitted for the 2.3-dev branch but it was merged into the 2.3 branch instead (closes #10326).

Discussion
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[HttpFoundation][Tests] Add tests for RequestStack class

| 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

Commits
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6f25d39 [HttpFoundation][Tests] Add tests for RequestStack class