chore: add autoload.exclude-from-classmap to suppress warnings

E.g.,
Class Laminas\Escaper\Escaper located in ./system/ThirdParty/Escaper/Escaper.php does not comply with psr-4 autoloading standard (rule: CodeIgniter\ => ./system). Skipping.

Author: kenjis

composer.json

@@ -64,7 +64,9 @@
             "CodeIgniter\\": "system/"
         },
         "exclude-from-classmap": [
-            "**/Database/Migrations/**"
+            "**/Database/Migrations/**",
+            "system/ThirdParty/**",
+            "tests/system/Config/fixtures/**"
         ]
     },
     "autoload-dev": {