Support symfony/cache and symfony/event-dispatcher 8 (#292)

Allow the dev-side Symfony components to install on v8, matching the
constraint widened for symfony/options-resolver in #291.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: neildaniels

composer.json

@@ -51,8 +51,8 @@
         "php-http/mock-client": "^1.2",
         "slevomat/coding-standard": "^8.27.1",
         "squizlabs/php_codesniffer": "^4.0.1",
-        "symfony/cache": "^4.4 || ^5 || ^6 || ^7",
-        "symfony/event-dispatcher": "^4.4 || ^5 || ^6 || ^7",
+        "symfony/cache": "^4.4 || ^5 || ^6 || ^7 || ^8",
+        "symfony/event-dispatcher": "^4.4 || ^5 || ^6 || ^7 || ^8",
         "phpstan/phpstan": "^2.1.38",
         "phpstan/phpstan-deprecation-rules": "^2.0.3",
         "spaze/phpstan-disallowed-calls": "^4.7.0",