Reducing mutation test core threshold

This patch reduces code size, therefore leading to
generally lower scores.

Until we completely switch to `pcov` and the upstream
issues with `sebastianbergmann/php-code-coverage`
are resolved, we will keep having sub-100% mutation
test scores.

Ref: sebastianbergmann/php-code-coverage#945
Ref: sebastianbergmann/php-code-coverage@c304be7
Ref: laminas/laminas-continuous-integration-action#130
Ref: sebastianbergmann/php-code-coverage#953

infection.json.dist

@@ -16,6 +16,6 @@
         "IdenticalEqual": false,
         "NotIdenticalNotEqual": false
     },
-    "minMsi": 90.3,
+    "minMsi": 90.1,
     "minCoveredMsi": 100
 }