Update guide for setting up PHP codespaces

[garrettw]

Why:

Closes: #44938

What's being changed (if available, include any code snippets, screenshots, or gifs):

Just updating the PHP image version to match the current default that will be chosen if the instructions are followed as written.

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

[github-actions]

How to review these changes 👓

Thank you for your contribution. To review these changes, choose one of the following options:

• Spin up a codespace
• Set up a local development environment

A Hubber will need to deploy your changes internally to review.

Table of review links

Note: Please update the URL for your staging server or codespace.

The table shows the files in the content directory that were changed in this pull request. This helps you review your changes on a staging server. Changes to the data directory are not included in this table.

Source	Review	Production	What Changed
codespaces/setting-up-your-project-for-codespaces/adding-a-dev-container-configuration/setting-up-your-php-project-for-codespaces.md	fpt ghec	fpt ghec

Key: fpt: Free, Pro, Team; ghec: GitHub Enterprise Cloud; ghes: GitHub Enterprise Server

🤖 This comment is automatically generated.

[Sharra-writes]

@garrettw Since I can see you wrote the original article and since these changes are minor, I'm just going to accept them without waiting for an SME to weigh in.

[github-actions]

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