Update symfony/var-exporter requirement from ^6.4||^7 to ^6.4||^7||^8

Updates the requirements on [symfony/var-exporter](https://github.com/symfony/var-exporter) to permit the latest version.
- [Release notes](https://github.com/symfony/var-exporter/releases)
- [Changelog](https://github.com/symfony/var-exporter/blob/7.3/CHANGELOG.md)
- [Commits](https://github.com/symfony/var-exporter/commits/v8.0.0)

---
updated-dependencies:
- dependency-name: symfony/var-exporter
  dependency-version: 8.0.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

composer.json

@@ -16,7 +16,7 @@
         "webonyx/graphql-php": "^v15.29",
         "psr/container": "^2.0",
         "league/event": "^3.0",
-        "symfony/var-exporter": "^6.4||^7"
+        "symfony/var-exporter": "^6.4||^7||^8"
     },
     "require-dev": {
         "doctrine/coding-standard": "^14.0",