feat: Update Cloud Functions samples to use non-EOL PHP

[bshaffer]

Some of our Cloud Functions samples still use PHP 7.4

• https://github.com/GoogleCloudPlatform/php-docs-samples/blob/add395fbcfb6cc55f3f638b025ddc3d6b6d31f59/functions/helloworld_storage/composer.json#L3
• https://github.com/GoogleCloudPlatform/php-docs-samples/blob/add395fbcfb6cc55f3f638b025ddc3d6b6d31f59/functions/typed_greeting/composer.json#L3
• https://github.com/GoogleCloudPlatform/php-docs-samples/blob/add395fbcfb6cc55f3f638b025ddc3d6b6d31f59/functions/helloworld_pubsub/composer.json#L3
• https://github.com/GoogleCloudPlatform/php-docs-samples/blob/add395fbcfb6cc55f3f638b025ddc3d6b6d31f59/functions/helloworld_http/composer.json#L3

As this version of PHP is now EOL, we need to upgrade these to the more current versions of PHP 8.2 or 8.3.