add type combinator tests

Addresses #3613 (comment), #3613 (comment)

Author: pmjones

tests/PHPStan/Type/TypeCombinatorTest.php

@@ -2050,6 +2050,14 @@ public function dataUnion(): iterable
 				UnionType::class,
 				'literal-string|uppercase-string',
 			],
+			[
+				[
+					new IntersectionType([new StringType(), new AccessoryLowercaseStringType()]),
+					new IntersectionType([new StringType(), new AccessoryUppercaseStringType()]),
+				],
+				UnionType::class,
+				'lowercase-string|uppercase-string',
+			],
 			[
 				[
 					TemplateTypeFactory::create(
@@ -4015,6 +4023,14 @@ public function dataIntersect(): iterable
 				IntersectionType::class,
 				'literal-string&uppercase-string',
 			],
+			[
+				[
+					new IntersectionType([new StringType(), new AccessoryLowercaseStringType()]),
+					new IntersectionType([new StringType(), new AccessoryUppercaseStringType()]),
+				],
+				IntersectionType::class,
+				'lowercase-string&uppercase-string',
+			],
 		];
 
 		if (PHP_VERSION_ID < 80100) {