fix: add safekeeper team to pgxn codeowners (#7170)

`pgxn/` also contains WAL proposer code, so modifications to this
directory should be able to be approved by the safekeeper team.

Signed-off-by: Alex Chi Z <chi@neon.tech>

CODEOWNERS

@@ -1,12 +1,13 @@
 /compute_tools/ @neondatabase/control-plane @neondatabase/compute
 /control_plane/attachment_service @neondatabase/storage
 /libs/pageserver_api/ @neondatabase/storage
-/libs/postgres_ffi/ @neondatabase/compute
+/libs/postgres_ffi/ @neondatabase/compute @neondatabase/safekeepers
 /libs/remote_storage/ @neondatabase/storage
 /libs/safekeeper_api/ @neondatabase/safekeepers
 /libs/vm_monitor/ @neondatabase/autoscaling
 /pageserver/ @neondatabase/storage
 /pgxn/ @neondatabase/compute
+/pgxn/neon/ @neondatabase/compute @neondatabase/safekeepers
 /proxy/ @neondatabase/proxy
 /safekeeper/ @neondatabase/safekeepers
 /vendor/ @neondatabase/compute