seastar: update submodule to wip-matanb-seastar-feb-26

```
Allow provided liburing builds via the URING::uring target.
This allows seastar, when built as a submodule, to use external
liburing.
```

https://github.com/ceph/seastar/tree/wip-matanb-seastar-feb26

Signed-off-by: Matan Breizman <mbreizma@redhat.com>

diff --git a/src/seastar b/src/seastar
index 7347cf6f4f966929d5dc5b3fd7e34d771c9b3f85..4936530fa8a649c075700a5d51fb90c436c80a62 160000 (submodule)
--- a/src/seastar
+++ b/src/seastar
@@ -1 +1 @@
-Subproject commit 7347cf6f4f966929d5dc5b3fd7e34d771c9b3f85
+Subproject commit 4936530fa8a649c075700a5d51fb90c436c80a62