Streaming websocket data into a table, blocks `INSERT INTO` data to this table from another source.

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Create two tables: table A and table B. Both table need to have the same schema.
2. Populate table B and leave table A empty.
3. Stream data into this table A via websocket (I do it via python).
4. While data is being saved into table A (multiple rows per second), try and INSERT INTO data from table B to table A.
5. Observe how it's not possible (i.e. the bug).

Expected behavior
I would expect to be able to write to a table with streaming data from multiple streams, via the UI and via other places too.

Screenshots
None.

Environment (please complete the following information):

• OS: Ubuntu 20.04.2 LTS (GNU/Linux 5.4.0-77-generic x86_64)
• Browser: chrome and safari
• Version: 6.0.4

Additional context
This issue became apparent following a Slack discussion here: https://questdb.slack.com/archives/C1NFJEER0/p1629298544172800

No files or tests are named. Reproduce with two same-schema tables, a Python websocket stream into the empty table, and a concurrent INSERT INTO from the second table; done means both write paths can continue successfully while streaming data is received.