Use assertNotSame when checking etags

Sometimes etags contain a "e" character which makes PHP believe it's a
number and make the tests fail

tests/lib/files/cache/changepropagator.php

@@ -65,8 +65,8 @@ class ChangePropagator extends \PHPUnit_Framework_TestCase {
 		$this->assertEquals($newInfo2->getMTime(), $time);
 		$this->assertEquals($newInfo3->getMTime(), $time);
 
-		$this->assertNotEquals($oldInfo1->getEtag(), $newInfo1->getEtag());
-		$this->assertNotEquals($oldInfo2->getEtag(), $newInfo2->getEtag());
-		$this->assertNotEquals($oldInfo3->getEtag(), $newInfo3->getEtag());
+		$this->assertNotSame($oldInfo1->getEtag(), $newInfo1->getEtag());
+		$this->assertNotSame($oldInfo2->getEtag(), $newInfo2->getEtag());
+		$this->assertNotSame($oldInfo3->getEtag(), $newInfo3->getEtag());
 	}
 }