[css-grid-1] Overflowing margin-aligned items should safe-align, just like flexbox (and implementations). Caught during review in #5923

Author: fantasai

css-grid-1/Overview.bs

@@ -3566,7 +3566,7 @@ Aligning with <a value for="margin">auto</a> margins</h3>
 
 		<li>
 			Overflowing [=grid items=] resolve their ''margin/auto'' margins to zero
-			and overflow as specified by their <a>box alignment properties</a>.
+			and ''justify-self/start''-align within their [=containing block=].
 	</ul>
 
 <h3 id='row-align'>