Document stricter infection test setup

Agent-Logs-Url: https://github.com/voku/Stringy/sessions/66d485bc-1215-40ee-be1b-89dc3284da01

Co-authored-by: voku <264695+voku@users.noreply.github.com>

Author: Copilot

.github/workflows/ci.yml

@@ -56,6 +56,7 @@ jobs:
             composer: basic
             phpunit: '^9.6'
             phpunit_config: phpunit.xml.dist
+    # Infection mutates and re-runs the suite, so that leg needs a longer timeout.
     timeout-minutes: ${{ matrix.run_infection && 30 || 10 }}
     steps:
       - name: Checkout code

tests/StaticStringyTest.php

@@ -59,6 +59,7 @@ public function testArgumentNumbers()
         $staticStringyClass = new ReflectionClass(S::class);
         $methodArgsProperty = $staticStringyClass->getProperty('methodArgs');
         $methodArgsProperty->setAccessible(true);
+        // Reset the cache so this test always exercises __callStatic()'s argument counting.
         $methodArgsProperty->setValue(null, null);
 
         S::slice('fòôbàř', 0, 3, 'UTF-8');