chore(deps-dev): bump heroku/heroku-buildpack-php in /tests/apps/php

Bumps [heroku/heroku-buildpack-php](https://github.com/heroku/heroku-buildpack-php) from 287 to 288.
- [Release notes](https://github.com/heroku/heroku-buildpack-php/releases)
- [Changelog](https://github.com/heroku/heroku-buildpack-php/blob/main/CHANGELOG.md)
- [Commits](https://github.com/heroku/heroku-buildpack-php/compare/v287...v288)

---
updated-dependencies:
- dependency-name: heroku/heroku-buildpack-php
  dependency-version: '288'
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

tests/apps/php/composer.lock

@@ -603,16 +603,16 @@
     "packages-dev": [
         {
             "name": "heroku/heroku-buildpack-php",
-            "version": "v287",
+            "version": "v288",
             "source": {
                 "type": "git",
                 "url": "https://github.com/heroku/heroku-buildpack-php.git",
-                "reference": "4f53d131bd04d41a1c6ab861d74fd1a16dbbf2cb"
+                "reference": "cb4b1671132119c7edba4278deb67a6517b4738f"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/heroku/heroku-buildpack-php/zipball/4f53d131bd04d41a1c6ab861d74fd1a16dbbf2cb",
-                "reference": "4f53d131bd04d41a1c6ab861d74fd1a16dbbf2cb",
+                "url": "https://api.github.com/repos/heroku/heroku-buildpack-php/zipball/cb4b1671132119c7edba4278deb67a6517b4738f",
+                "reference": "cb4b1671132119c7edba4278deb67a6517b4738f",
                 "shasum": ""
             },
             "bin": [
@@ -642,9 +642,9 @@
             ],
             "support": {
                 "issues": "https://github.com/heroku/heroku-buildpack-php/issues",
-                "source": "https://github.com/heroku/heroku-buildpack-php/tree/v287"
+                "source": "https://github.com/heroku/heroku-buildpack-php/tree/v288"
             },
-            "time": "2026-04-17T14:51:42+00:00"
+            "time": "2026-05-12T13:03:49+00:00"
         }
     ],
     "aliases": [],