minor #50297 Remove unnecessary usages of DateTime (nicolas-grekas)

This PR was merged into the 6.4 branch.

Discussion
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Remove unnecessary usages of DateTime

| Q             | A
| ------------- | ---
| Branch?       | 6.3
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | Part of #47580
| License       | MIT
| Doc PR        | -

Together with #50290, this PR removes `DateTime` everywhere possible.

What remains is:
- test cases that test both DateTime and DateTimeImmutable - legit to keep
- date/time form-types and transformers in the Form component - we'd need a separate effort for them, related to #50295
- `PersistentTokenInterface::getLastUsed(): \DateTime` - separate effort also

Commits
-------

8b08294b63 Remove unnecessary usages of DateTime

Author: fabpot

Command/AboutCommand.php

@@ -80,7 +80,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
             ['Version', \PHP_VERSION],
             ['Architecture', (\PHP_INT_SIZE * 8).' bits'],
             ['Intl locale', class_exists(\Locale::class, false) && \Locale::getDefault() ? \Locale::getDefault() : 'n/a'],
-            ['Timezone', date_default_timezone_get().' (<comment>'.(new \DateTime())->format(\DateTime::W3C).'</>)'],
+            ['Timezone', date_default_timezone_get().' (<comment>'.(new \DateTimeImmutable())->format(\DateTimeInterface::W3C).'</>)'],
             ['OPcache', \extension_loaded('Zend OPcache') && filter_var(\ini_get('opcache.enable'), \FILTER_VALIDATE_BOOL) ? 'true' : 'false'],
             ['APCu', \extension_loaded('apcu') && filter_var(\ini_get('apc.enabled'), \FILTER_VALIDATE_BOOL) ? 'true' : 'false'],
             ['Xdebug', \extension_loaded('xdebug') ? 'true' : 'false'],