[Php81] Skip Encapsed on NullToStrictStringFuncCallArgRector (#2744)

* Add failing test fixture for NullToStrictStringFuncCallArgRector

# Failing Test for NullToStrictStringFuncCallArgRector

Based on https://getrector.org/demo/b778fb29-98e6-4992-b4fa-b14a0be26429

In this case, the first argument of the mb_strlen function cannot be something else than a string, so the cast to string is useless

* Closes #2742

Co-authored-by: Grégoire Pineau <lyrixx@lyrixx.info>

rules-tests/Php81/Rector/FuncCall/NullToStrictStringFuncCallArgRector/Fixture/skip_encapsed.php.inc

@@ -0,0 +1,13 @@
+<?php
+
+namespace Rector\Tests\Php81\Rector\FuncCall\NullToStrictStringFuncCallArgRector\Fixture;
+
+final class SkipEncapsed
+{
+    public function foo(string $bar): array
+    {
+        mb_strlen("foo:{$bar}:");
+    }
+}
+
+?>

rules/Php81/Rector/FuncCall/NullToStrictStringFuncCallArgRector.php

@@ -13,6 +13,7 @@
 use PhpParser\Node\Expr\FuncCall;
 use PhpParser\Node\Expr\MethodCall;
 use PhpParser\Node\Identifier;
+use PhpParser\Node\Scalar\Encapsed;
 use PhpParser\Node\Scalar\String_;
 use PhpParser\Node\Stmt\Trait_;
 use PHPStan\Analyser\Scope;
@@ -408,6 +409,10 @@ private function processNullToStrictStringOnNodePosition(
             return null;
         }
 
+        if ($argValue instanceof Encapsed) {
+            return null;
+        }
+
         if ($this->isAnErrorTypeFromParentScope($argValue)) {
             return null;
         }