Bump veewee/xml minimum to ^3.6

veewee/xml 3.6.0 is the first version that replaced azjezz/psl with
php-standard-library/php-standard-library, preventing class conflicts
when resolving with --prefer-lowest.

Author: veewee

composer.json

@@ -19,7 +19,7 @@
         "php-soap/engine": "^2.19",
         "php-soap/wsdl": "^1.18",
         "php-soap/xml": "^1.9.0",
-        "veewee/xml": "^3.0",
+        "veewee/xml": "^3.6",
         "php-standard-library/php-standard-library": "^3.0 || ^4.0 || ^5.0 || ^6.0",
         "symfony/console": "^5.4 || ^6.0 || ^7.0 || ^8.0",
         "webmozart/assert": "^1.11",