…on PHP 7.4 (alexpott)This PR was squashed before being merged into the 3.4 branch (closes#34097).Discussion----------[Validator] Ensure numeric subpaths do not cause errors on PHP 7.4| Q             | A| ------------- | ---| Branch?       | 3.4| Bug fix?      | yes| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->| Tickets       | Fix #... <!-- prefix each issue number with "Fix #", if any -->| License       | MIT| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->Drupal is testing on PHP7.4 and hitting a problem with the line `if ('[' === $subPath[0]) {` because `$subPath` is not a string. We're already doing string casting in the method so we could do it once and be done. Note this is not a problem on the master branch / SF5 because of primitive typehinting.Without this fix on PHP7.4 you see errors like...```1) Symfony\Component\Validator\Tests\Util\PropertyPathTest::testAppend with data set#5 ('0', 1, '0.1', 'Numeric subpaths do not cause...rrors.')Trying to access array offset on value of type int```Commits-------6244a1e [Validator] Ensure numeric subpaths do not cause errors on PHP 7.4