fix(ci): align S3 KMS fixtures and default key expectations (#7573)

.github/s3tests/s3tests.conf

@@ -55,6 +55,10 @@ secret_key = ${S3_SECRET_KEY}
 
 ## replace with key id obtained when secret is created, or delete if KMS not tested
 #kms_keyid = 01234567-89ab-cdef-0123-456789abcdef
+#kms_keyid2 = fedcba98-7654-3210-fedc-ba9876543210
+
+## Expected service default for SSE-KMS requests without a key id; empty means none
+#kms_default_keyid =
 
 ## Storage classes
 #storage_classes = "LUKEWARM, FROZEN"