Appoint release shepherds for v2.52 and v2.53

Note that we have delayed v2.52 by a week to avoid collisions with
events and travels.

Signed-off-by: beorn7 <beorn@grafana.com>

RELEASE.md

@@ -56,6 +56,8 @@ Release cadence of first pre-releases being cut is 6 weeks.
 | v2.49          | 2023-12-05                                 | Bartek Plotka (GitHub: @bwplotka)           |
 | v2.50          | 2024-01-16                                 | Augustin Husson (GitHub: @nexucis)          |
 | v2.51          | 2024-03-07                                 | Bryan Boreham (GitHub: @bboreham)           |
+| v2.52          | 2024-04-22                                 | Arthur Silva Sens (GitHub: @ArthurSens)     |
+| v2.53          | 2024-06-03                                 | George Krajcsovits (GitHub: @krajorama)     |
 
 If you are interested in volunteering please create a pull request against the [prometheus/prometheus](https://github.com/prometheus/prometheus) repository and propose yourself for the release series of your choice.