Temporary forbid support for symfony/error-handler

This mitigate the following deprecation #72 (comment)
This could be reverted once sebastianbergmann/php-file-iterator#74
is merged and released.

Note that this does not forbid the component in version 6, but in this
case, PHP 8.0 is required, and so the attribute is not ignored.

composer.json

@@ -26,7 +26,8 @@
         "symfony/yaml": "^3.4.26|^4.1.12|^5.0"
     },
     "conflict": {
-        "ext-apc": "3.1.11"
+        "ext-apc": "3.1.11",
+        "symfony/error-handler": "5.4.*"
     },
     "autoload": {
         "psr-4": { "JoliTypo\\": "src/JoliTypo" }