Fix PHPStan 1.12.2

[Alkarex]

CI breaks because upstream does not pin composer.lock...

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  Line   src/IRI.php
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  :304   Offset 3 on array{0: string, 1: '', scheme: null, 2: string, 3: string, authority: string, 4: string, path: string, ...}|array{0: string, 1: non-empty-string, scheme: string, 2: string, 3: string, authority: string, 4: string, path: string, ...} in isset()
         always exists and is not nullable.
  :307   Offset 5 on array{0: string, 1: '', scheme: null, 2: string, 3: string, authority: string|null, 4: string, path: string, ...}|array{0: string, 1: non-empty-string, scheme: string, 2: string, 3: string, authority: string|null, 4: string, path: string, ...}
         in isset() always exists and is not nullable.
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