fix: Add missing webmozart/assert (#39)

I am not convinced this is really needed and in general I think the less
dependencies the better.

Nonetheless the assert was installed as a transitive dependency before
and no longer is resulting in our code failing.

Author: theofidry

composer.json

@@ -34,7 +34,8 @@
         "infection/include-interceptor": "^0.2.0",
         "symfony/filesystem": "^6.4 || ^7.4",
         "symfony/process": "^6.4 || ^7.4",
-        "symfony/yaml": "^6.4 || ^7.4"
+        "symfony/yaml": "^6.4 || ^7.4",
+        "webmozart/assert": "^2.0"
     },
     "extra": {
         "infection": {