Skip SIG Std/Cert on May 21st due to the SCS Summit 2026 (#434)

Likely most if not all participants will be at the SCS Summit.

Signed-off-by: Felix Kronlage-Dammers <fkr@hazardous.org>

Author: fkr

teams/sig_standard_cert/team_meetings.yml

@@ -87,3 +87,4 @@ events:
       until: 2026-12-18
       except_on:
         - 2026-02-26 14:05:00  # Yaook-SCS-operator Hackathon
+        - 2026-05-21 14:05:00  # SCS Summit 2026