[CODEOWNER] Update unified runtime plug-in code owner (#8659)

Make @intel/dpcpp-l0-pi-reviewers the owner of UR while it is not moved
into a separate repo.

Signed-off-by: Sergey V Maslov <[email protected]>

Author: smaslov-intel

.github/CODEOWNERS

@@ -37,6 +37,9 @@ sycl/doc/extensions/ @intel/dpcpp-specification-reviewers
 # Level Zero plugin
 sycl/plugins/level_zero/ @intel/dpcpp-l0-pi-reviewers
 
+# Unified Runtime plugin
+sycl/plugins/unified_runtime/ @intel/dpcpp-l0-pi-reviewers
+
 # ESIMD CPU emulator plug-in
 sycl/plugins/esimd_emulator/ @intel/dpcpp-esimd-reviewers