Update .gitattributes

PHP Coding-style fixer config not required for package installation.

Similarly with the changelog.md, the history of changes can be viewed in git.

Author: KarelWintersky

.gitattributes

@@ -10,4 +10,6 @@ tests               export-ignore
 vendor              export-ignore
 actions.phpunit.xml export-ignore
 phpstan.phar        export-ignore
-phpstan.neon        export-ignore
+phpstan.neon        export-ignore
+.php-cs-fixer.dist.php export-ignore
+CHANGELOG.md        export-ignore