align a return type in collections internals with Scala 3

SethTisue · SethTisue · commit cbce2011218e · 2023-09-20T15:00:50.000+02:00
context: scala#18525, which upgrades Scala 3 to use the 2.13.12 stdlib; MiMa there is complaining
diff --git a/library/src/scala/collection/immutable/HashMap.scala b/library/src/scala/collection/immutable/HashMap.scala
@@ -2181,7 +2181,7 @@ private final class MapNodeRemoveAllSetNodeIterator[K](rootSetNode: SetNode[K])
     curr
   }
 
-  override def next() = Iterator.empty.next()
+  override def next(): K = Iterator.empty.next()
 }
 
 /**

Original file line number	Diff line number	Diff line change
`@@ -2181,7 +2181,7 @@ private final class MapNodeRemoveAllSetNodeIterator[K](rootSetNode: SetNode[K])`
`2181`	`2181`	`curr`
`2182`	`2182`	`}`
`2183`	`2183`
`2184`		`- override def next() = Iterator.empty.next()`
	`2184`	`+ override def next(): K = Iterator.empty.next()`
`2185`	`2185`	`}`
`2186`	`2186`
`2187`	`2187`	`/**`