Update guzzlehttp/guzzle in changelog-generator to v8

http-interop/http-factory-guzzle does not allow guzzlehttp/psr7 3. It is
not needed: php-http/discovery finds the PSR-17 factories in
guzzlehttp/psr7 itself.

Amp-Thread-ID: https://ampcode.com/threads/T-01a176c6-528a-7430-b296-e66930d153b4

Author: ondrejmirtes

changelog-generator/composer.json

@@ -4,8 +4,7 @@
 		"php": "^8.4",
 		"php-http/client-common": "^2.5",
 		"php-http/discovery": "^1.14",
-		"guzzlehttp/guzzle": "^7.4",
-		"http-interop/http-factory-guzzle": "^1.2",
+		"guzzlehttp/guzzle": "^8.0",
 		"knplabs/github-api": "^3.7",
 		"symfony/console": "^8.1"
 	},