conncache: Fix cancellation leaks upon close.

Change-Id: I3f951cab94423fb43fd36d78112f50367e97dc54
diff --git a/runtime/internal/flow/manager/conncache.go b/runtime/internal/flow/manager/conncache.go
index 3bd8654..72e66c0 100644
--- a/runtime/internal/flow/manager/conncache.go
+++ b/runtime/internal/flow/manager/conncache.go
@@ -466,6 +466,14 @@
 	err := NewErrCacheClosed(ctx)
 	for _, e := range c.conns {
 		e.conn.Close(ctx, err)
+		if e.cancel != nil {
+			e.cancel()
+		}
+	}
+	for _, r := range c.reserved {
+		if r.cancel != nil {
+			r.cancel()
+		}
 	}
 	c.conns = nil
 	c.cache = nil