persist,test: increase timeout on failpoint test

I did observe this failing when running it manually in a loop, but the
dataflow would catch up eventually, which I checked by running a
`SELECT` query by hand. This means it's not the bug that we fixed in
#10128

We've also seen it at least once in ci builds.

Author: aljoscha

test/persistence/kafka-sources/failpoint-after.td

@@ -7,6 +7,9 @@
 # the Business Source License, use of this software will be governed
 # by the Apache License, Version 2.0.
 
+# Reading all that data after starting up can take longer than the default timeout.
+$ set-sql-timeout duration=60s
+
 > SELECT COUNT(*) FROM failpoint;
 1000000