Fix dynamic variable access producing inconsistent errors on PHP 8.1+

Use getScopeType() instead of getType() in filterBySpecifiedTypes() to
bypass the fiber mechanism when reading the narrowed type after
addTypeToExpression/assignExpression. On FiberScope, getType() suspends
the fiber and returns the pre-modification type from the coordinator,
causing conditional expression guard matching to fail. This made $$name
dynamic access report false "might not be defined" errors for variables
that are conditionally defined based on the name value.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

src/Analyser/MutatingScope.php

@@ -3230,7 +3230,7 @@ public function filterBySpecifiedTypes(SpecifiedTypes $specifiedTypes): self
 			} else {
 				$scope = $scope->removeTypeFromExpression($expr, $type);
 			}
-			$specifiedExpressions[$typeSpecification['exprString']] = ExpressionTypeHolder::createYes($expr, $scope->getType($expr));
+			$specifiedExpressions[$typeSpecification['exprString']] = ExpressionTypeHolder::createYes($expr, $scope->getScopeType($expr));
 		}
 
 		$conditions = [];

tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php

@@ -1137,14 +1137,6 @@ public function testDynamicAccess(): void
 				'Undefined variable: $buz',
 				49,
 			],
-			[
-				'Variable $bar might not be defined.',
-				49,
-			],
-			[
-				'Variable $foo might not be defined.',
-				49,
-			],
 			[
 				'Variable $foo might not be defined.',
 				50,