composer(deps-dev): bump phpunit/phpunit from 8.5.8 to 8.5.13

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 8.5.8 to 8.5.13.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-8.5.md)
- [Commits](sebastianbergmann/phpunit@8.5.8...8.5.13)

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

composer.json

@@ -26,7 +26,7 @@
     "require-dev": {
         "ext-intl": "*",
         "dealerdirect/phpcodesniffer-composer-installer": "~0.7.0",
-        "phpunit/phpunit": "^8.5.8",
+        "phpunit/phpunit": "^8.5.13",
         "slevomat/coding-standard": "^6.4.1",
         "squizlabs/php_codesniffer": "^3.5.8"
     },