workflow: update maintainers

Author: 0xc0170

docs/reference/contributing/guidelines/workflow.md

@@ -22,8 +22,8 @@ The current maintainers are:
 - [Martin Kojtal](https://os.mbed.com/users/Kojto).
 - [Jimmy Brisson](https://os.mbed.com/users/theotherjimmy).
 - [Shrikant Tudavekar](https://os.mbed.com/users/shrikant1213).
-- [Sam Grove](https://os.mbed.com/users/sam_grove).
-- [Cruz Monrreal](https://os.mbed.com/users/MrCruz).
+- [Nir Sonnenschein](https://os.mbed.com/users/nirs).
+- [Cruz Monrreal](https://os.mbed.com/users/CM2).
 - [Kevin Bracey](https://os.mbed.com/users/kjbracey).
 
 ### Contributions