Deduplicate bug-8270 and bug-13623 test files

Point IfConstantConditionRuleTest and NullCoalesceRuleTest to the
existing nsrt test files instead of maintaining duplicate copies.

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

Author: phpstan-bot

tests/PHPStan/Rules/Comparison/IfConstantConditionRuleTest.php

@@ -216,7 +216,7 @@ public function testBug4284(): void
 	public function testBug8270(): void
 	{
 		$this->treatPhpDocTypesAsCertain = true;
-		$this->analyse([__DIR__ . '/data/bug-8270.php'], []);
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-8270.php'], []);
 	}
 
 }

tests/PHPStan/Rules/Comparison/data/bug-8270.php

@@ -379,7 +379,7 @@ public function testBug13921(): void
 
 	public function testBug13623(): void
 	{
-		$this->analyse([__DIR__ . '/data/bug-13623.php'], []);
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-13623.php'], []);
 	}
 
 }