TimeoutError when calling asyncpg.create_pool()

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* **asyncpg version**: 0.24.0
* **PostgreSQL version**: 12
* **Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
the issue with a local PostgreSQL install?**: no SaaS
* **Python version**: 3.9.7
* **Platform**: Linux/Docker (image python:3.9-slim)
* **Do you use pgbouncer?**: No
* **Did you install asyncpg with pip?**: Yes
* **If you built asyncpg locally, which version of Cython did you use?**: n/a
* **Can the issue be reproduced under both asyncio and
[uvloop](https://github.com/magicstack/uvloop)?**: Issue happens with both, though the below error is with uvloop

DISCLAIMER: I am relatively new to async methodologies in Python (I am primary a C# engineer), so I may be doing something completely wrong. Feel free to point anything out! Thats how we learn right? haha

I seem to get the below exception a few times an hour. I am relatively certain its not any kind of connection exhaustion as I am using `async with` statements like those in documentation, and other apps that use this DB are unaffected, this is the 1st app to use asyncpg.

Stack Trace:
```
Traceback (most recent call last):
File "/usr/local/lib/python3.9/site-packages/asyncpg/connect_utils.py", line 586, in _create_ssl_connection
tr, pr = await loop.create_connection(
File "uvloop/loop.pyx", line 2014, in create_connection
File "uvloop/loop.pyx", line 2001, in uvloop.loop.Loop.create_connection
asyncio.exceptions.CancelledError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/local/lib/python3.9/asyncio/tasks.py", line 492, in wait_for
fut.result()
asyncio.exceptions.CancelledError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "/app/./scripts/scheduler_ahs.py", line 28, in process_ah
ah_processor = await AHProcessor.create(ah_id)
File "/app/scripts/process_ah.py", line 39, in create
db = await Database.create()
File "/app/lib/db.py", line 13, in create
pool = await asyncpg.create_pool(
File "/usr/local/lib/python3.9/site-packages/asyncpg/pool.py", line 407, in _async__init__
await self._initialize()
File "/usr/local/lib/python3.9/site-packages/asyncpg/pool.py", line 445, in _initialize
await asyncio.gather(*connect_tasks)
File "/usr/local/lib/python3.9/site-packages/asyncpg/pool.py", line 127, in connect
self._con = await self._pool._get_new_connection()
File "/usr/local/lib/python3.9/site-packages/asyncpg/pool.py", line 491, in _get_new_connection
con = await connect_utils._connect_addr(
File "/usr/local/lib/python3.9/site-packages/asyncpg/connect_utils.py", line 676, in _connect_addr
return await __connect_addr(params, timeout, True, *args)
File "/usr/local/lib/python3.9/site-packages/asyncpg/connect_utils.py", line 720, in __connect_addr
tr, pr = await compat.wait_for(connector, timeout=timeout)
File "/usr/local/lib/python3.9/site-packages/asyncpg/compat.py", line 66, in wait_for
return await asyncio.wait_for(fut, timeout)
File "/usr/local/lib/python3.9/asyncio/tasks.py", line 494, in wait_for
raise exceptions.TimeoutError() from exc
asyncio.exceptions.TimeoutError
```

I am using a DB wrapper class. In my actual app I create an instance of the below class and then call the close_pool() method when my app is done using the database.
```
class Database:
def __init__(self, pool: asyncpg.Pool) -> None:
self._pool = pool

@classmethod
async def create(cls, num_connections=3):
pool = await asyncpg.create_pool(
dsn=my_conn_string,
server_settings={"search_path": my_schema},
min_size=num_connections,
max_size=num_connections,
)
return cls(pool)

async def fetch(self, sql, *args):
async with self._pool.acquire() as connection:
return await connection.fetch(sql, *args)

async def fetch_as_dataframe(self, sql, *args):
async with self._pool.acquire() as connection:
stmt = await connection.prepare(sql)
columns = [a.name for a in stmt.get_attributes()]
data = await stmt.fetch(*args)
return pd.DataFrame(data, columns=columns)

async def fetchrow(self, sql, *args):
async with self._pool.acquire() as connection:
return await connection.fetchrow(sql, *args)

async def execute(self, sql, *args):
async with self._pool.acquire() as connection:
return await connection.execute(sql, *args)

async def copy_records_to_table(self, table, records):
async with self._pool.acquire() as connection:
return await connection.copy_records_to_table(table, records=records)

async def close_pool(self):
await self._pool.close()
```

Beginne mit dem gemeldeten Stack Trace in asyncpg.create_pool() und den angegebenen Versionen, der Plattform und den Pool-Einstellungen. Reproduziere das Timeout unter Python 3.9, PostgreSQL 12 sowie mit asyncio und uvloop, und untersuche anschließend den in asyncpg/connect_utils.py und asyncpg/pool.py gezeigten Pfad zum Einrichten der Verbindung. Erledigt ist die Aufgabe, wenn eine reproduzierbare Ursache identifiziert und das Timeout-Verhalten dokumentiert oder behoben wurde.

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