release_schedule: Add release manager to 5.43.6

Author: thibaultduponchelle

Porting/release_schedule.pod

@@ -48,7 +48,7 @@ you should reset the version numbers to the next blead series.
   2025-09-20  5.43.3
   2025-10-20  5.43.4          Max Maischein
   2025-11-20  5.43.5          Thibault Duponchelle
-  2025-12-20  5.43.6
+  2025-12-20  5.43.6          Steve Hay
   2026-01-20  5.43.7          Thibault Duponchelle
   2026-02-20  5.43.8                            Contentious changes freeze
   2026-03-20  5.43.9                            User-visible changes to