Blacklist new sytest validation test (#11270)

changelog.d/11270.misc

@@ -0,0 +1 @@
+Blacklist new SyTest that checks that key uploads are valid pending the validation being implemented in Synapse.

sytest-blacklist

@@ -32,3 +32,6 @@ We can't peek into rooms with invited history_visibility
 We can't peek into rooms with joined history_visibility
 Local users can peek by room alias
 Peeked rooms only turn up in the sync for the device who peeked them
+
+# Validation needs to be added to Synapse: #10554
+Rejects invalid device keys