#838 update composer dev dependencies

[PANawkar]

#838
Implemented:
dealerdirect/phpcodesniffer-composer-installer ^1.2
PHPUnit refresh constrained to ^8.5.x
yoast/phpunit-polyfills ^4.0
Updated composer.lock

Set config.platform.php to 7.2.24 to ensure compatibility with wp-env PHPUnit runs on PHP 7.2.

Deferred Updates
The following upgrades are deferred:
spatie/phpunit-watcher ^1.24
szepeviktor/phpstan-wordpress ^2
phpstan/phpstan ^2

These require PHP 8.1+ / Symfony 6, which introduces PHP 8-only syntax into vendor/ and breaks the current single-vendor, multi-PHP CI matrix.

[github-actions]

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[nimesh-xecurify]

Could you check if you are able to generate test coverage report with this configuration on PHP 8+? I faced some difficulties in my recent PR #856