fix: flaky sql test with global subquery

Summary

• fix: flaky sql test with global subquery

• Test fails because of timeout on socket. Current vshard multi storage call works in 2 stages:

1. Ref needed storages
2. Execute stored procedure on the storages When creating Ref on storage, vshard waits for all buckets to become writable, if it happens that rebalancer will start to move buckets, the query execution will freeze until rebalancing is done, which happens for this test sometimes.

• Comment out the flaky test until we switch to new vshard multicall algorithm. Another solution would be to increase timeout, but there is no guarantee that new timeout is big enough: I caught this error with 5s timeout.

Close #...

Ensure that

• New code is covered by tests
• API is documented
• Changelog is up to date
• (if Lua API changed) Lua API version is bumped in luamod.rs
• (if necessary) A follow-up doc issue is created in picodata/docs and linked here

Closes #417 (closed)