add shadows

Author: npolshakova

communication/slack-config/sig-release/usergroups.yaml

@@ -55,9 +55,12 @@ usergroups:
       - gracenng            # Release Team Subproject Lead
       - katcosgrove         # Release Team Subproject Lead
       - neoaggelos          # 1.33 Emeritus Advisor
+      - mbianchidev         # 1.33 Release Lead Shadow
       - npolshakova         # 1.33 Release Lead
+      - rashansmith         # 1.33 Release Lead Shadow
       - rayandas            # 1.33 Docs Lead
       - rytswd              # 1.33 Communications Lead
+      - sanchita-07         # 1.33 Release Lead Shadow
       - Vyom-Yadav          # 1.33 Release Lead Shadow
 
   # Should match SIG Release Leads at all times: