Switched local var to deepcopy

Author: zasweq

internal/transport/http2_client.go

@@ -1233,7 +1233,11 @@ func (t *http2Client) handleGoAway(f *http2.GoAwayFrame) {
 		upperLimit = math.MaxUint32 // Kill all streams after the GoAway ID.
 	}
 
-	activeStreams := t.activeStreams
+	activeStreams := make(map[uint32]*Stream)
+	for streamID, stream  := range t.activeStreams {
+		activeStreams[streamID] = stream
+	}
+
 	t.prevGoAwayID = id
 	t.mu.Unlock()
 	for streamID, stream := range activeStreams {