Generic/DisallowYodaConditions: ?? should not trigger the sniff

This commit changes the DisallowYodaConditions sniff so that the null
coalescing operator (`??`) does not trigger it.

src/Standards/Generic/Sniffs/ControlStructures/DisallowYodaConditionsSniff.php

@@ -25,7 +25,10 @@ class DisallowYodaConditionsSniff implements Sniff
      */
     public function register()
     {
-        return Tokens::$comparisonTokens;
+        $tokens = Tokens::$comparisonTokens;
+        unset($tokens[T_COALESCE]);
+
+        return $tokens;
 
     }//end register()
 

src/Standards/Generic/Tests/ControlStructures/DisallowYodaConditionsUnitTest.inc

@@ -173,3 +173,5 @@ echo match ($text) {
     'foo' => 10 === $y,
     10 === $y => 'bar',
 };
+
+1 ?? $nullCoalescingShouldNotTriggerSniff;