Something is setting the result on a completed task?

Nobody has claimed this yet.

* **asyncpg version**: 0.22.0+ (at commit 075114c195e9eb4e81c8365d81540beefb46065c)
* **PostgreSQL version**: CockroachDB v20.2.3
* **Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
the issue with a local PostgreSQL install?**: not a SaaS, we do our own deployments
* **Python version**: Python 3.9.1
* **Platform**: Linux
* **Do you use pgbouncer?**: no
* **Did you install asyncpg with pip?**: yes but from the git repo, to get the latest fixes
* **If you built asyncpg locally, which version of Cython did you use?**:
* **Can the issue be reproduced under both asyncio and
[uvloop](https://github.com/magicstack/uvloop)?**: for now I've seen this under uvloop

```Fatal error on transport TCPTransport
protocol:
transport:
Traceback (most recent call last):
File "uvloop/handles/stream.pyx", line 829, in uvloop.loop.__uv_stream_on_read_impl
File "/root/aurora-extract/src/asyncpg/asyncpg/connect_utils.py", line 516, in data_received
self.on_data.set_result(True)
asyncio.exceptions.InvalidStateError: invalid state```

Start at asyncpg/connect_utils.py:516, where TLSUpgradeProto.data_received calls self.on_data.set_result(True), and trace when that task is completed under uvloop. Reproduce the reported InvalidStateError with CockroachDB if possible; done means the TLS upgrade no longer attempts to set a result on an already-completed task.

Written by the indexing model from the issue text.