Fix unknown tags in some scaladocs

Author: danicheg

core/shared/src/main/scala/fs2/Stream.scala

@@ -4035,9 +4035,9 @@ object Stream extends StreamLowPriority {
       * or from the observer pipe (when applied to source chunks) will cause the
       * termination of the resulting stream, and will be raised from this.
       *
-      * @returns A stream that may emit the same outputs as this stream (source),
-      *          in the same order and chunks, and performs the same effects as
-      *          the source; but in which every chunk is processed by the pipe.
+      * @return A stream that may emit the same outputs as this stream (source),
+      *         in the same order and chunks, and performs the same effects as
+      *         the source; but in which every chunk is processed by the pipe.
       */
     def observeAsync(
         maxQueued: Int

core/shared/src/main/scala/fs2/internal/Scope.scala

@@ -303,7 +303,7 @@ private[fs2] final class Scope[F[_]] private (
     go(self, Chain.empty)
   }
 
-  /** @returns true if the given `scopeId` identifies an ancestor of this scope, or false otherwise.
+  /** @return true if the given `scopeId` identifies an ancestor of this scope, or false otherwise.
     */
   def descendsFrom(scopeId: Unique.Token): Boolean = findSelfOrAncestor(scopeId).isDefined