[Hello World Tutorial] Bump Php alpine docker image version to 8.4.2-alpine3.21

[github-actions]

Bumps the php docker images versions for the Hello World! tutorial

Update the value of the php docker image for pipelines in the 'Hello World!' tutorial

1 file(s) updated with "${1}php:8.4.2-alpine3.21${3}": * content/doc/pipeline/tour/hello-world.adoc

8.3.15

Release published on the 2024-12-20 01:15:38 +0000 UTC at the url https://github.com/php/php-src/releases/tag/php-8.3.15

The PHP development team announces the immediate availability of PHP 8.3.15. This is a bug fix release.

All PHP 8.3 users are encouraged to upgrade to this version.

For source downloads of PHP 8.3.15 please visit our [downloads page](https://www.php.net/downloads.php), Windows source and binaries can be found on [windows.php.net/download/](https://windows.php.net/download/). The list of changes is recorded in the [ChangeLog](https://www.php.net/ChangeLog-8.php#8.3.15).

GitHub Action workflow link

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[MarkEWaite]

@dependabot squash and merge