MAINTAINERS: Fix label for 'nRF52 BSIM'

This commit updates the label name in the 'nRF52 BSIM' entry to match
the actual GitHub label name, which is 'platform: nRF52 BSIM'.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

MAINTAINERS.yml

@@ -1356,7 +1356,7 @@ nRF52 BSIM:
     files:
         - boards/posix/nrf52_bsim/
     labels:
-        - "platform: nrf52_bsim"
+        - "platform: nRF52 BSIM"
 
 POSIX API layer:
     status: odd fixes