chore(deps): bump guzzlehttp/guzzle in /tests/php_test_files (#91)

Bumps [guzzlehttp/guzzle](https://github.com/guzzle/guzzle) from 6.5.8 to 7.12.1.
- [Release notes](https://github.com/guzzle/guzzle/releases)
- [Changelog](https://github.com/guzzle/guzzle/blob/7.12/CHANGELOG.md)
- [Commits](guzzle/guzzle@6.5.8...7.12.1)

---
updated-dependencies:
- dependency-name: guzzlehttp/guzzle
  dependency-version: 7.12.1
  dependency-type: direct:production
...

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Author: dependabot[bot]

tests/php_test_files/composer.json

@@ -3,7 +3,7 @@
   "prefer-stable": true,
   "require": {
     "ext-curl": "*",
-    "guzzlehttp/guzzle": "^6.5",
+    "guzzlehttp/guzzle": "^7.12",
     "nyholm/psr7": "^1.5",
     "spiral/roadrunner-http": "^3.0",
     "spiral/roadrunner-worker": "^3.0",