Bump phpunit/phpunit from 7.3.5 to 8.5.52 in /_integration/php

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 7.3.5 to 8.5.52.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/8.5.52/ChangeLog-8.5.md)
- [Commits](sebastianbergmann/phpunit@7.3.5...8.5.52)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-version: 8.5.52
  dependency-type: direct:development
...

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

Author: dependabot[bot]

_integration/php/composer.json

@@ -7,6 +7,6 @@
         ]
     },
     "require-dev": {
-        "phpunit/phpunit": "^7"
+        "phpunit/phpunit": "^8"
     }
 }