[VarDumper] fix and test PdoCaster
bug #13073 [VarDumper] fix and test PdoCaster (nicolas-grekas)

This PR was merged into the 2.6 branch.

Discussion
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[VarDumper] fix and test PdoCaster

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #13042
| License       | MIT
| Doc PR        | -

Commits
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0b1be13 [VarDumper] fix and test PdoCaster