SIGSEGV from OpenSSL when used in async context
### Description

While performing many queries in a row to our API the code at some point errors out with a SIGSEGV. This comes from `ssl3_read_bytes` which in turn is called from https://github.com/nim-lang/Nim/blob/version-2-0/lib/pure/asyncnet.nim#L328. Starting each `AsyncHttpClient` with their own `SSLContext` seems to have helped somewhat, but the error still occurs occasionally. My best guess is that there is some condition where SSL needs some extra care that `AsyncHttpClient` doesn't provide, and this corrupts the `SSLContext` leading to the SIGSEGV. But that is just speculation based on the fact that this only happens sometimes.

### Nim Version

Tested with 2.0.8

### Current Output
This is a backtrace from GDB when the crash happens, line 112 in `mycode.nim` (redacted name and SSL buffer contents) is a call to `waitFor` on multiple connections combined with `all`.

```text
#0  0x00007ffff7c39e4a in ssl3_read_bytes (ssl=<optimized out>, type=23 '\027', recvd_type=0x0, 
    buf=0x7ffff7ba3046 "<data>"..., len=4000, peek=0, readbytes=0x7fffffffd030) at ssl/record/rec_layer_s3.c:687
#1  0x00007ffff7be6989 in ssl3_read_internal (s=0x5555560006f0, buf=0x7ffff7ba3046, len=4000, peek=0, 
    readbytes=0x7fffffffd030) at ssl/s3_lib.c:4527
#2  0x00007ffff7bee56b in SSL_read (s=<optimized out>, buf=<optimized out>, num=<optimized out>) at ssl/ssl_lib.c:2328
#3  0x00005555555cdc96 in _ZN4recv19recvX20X28AsyncX29_E (ClE_0=0x7fffeab86280)
    at /home/peter/.choosenim/toolchains/nim-2.0.8/lib/pure/asyncnet.nim:328
#4  0x00005555555c92f7 in _ZN4recv20recvNimAsyncContinueE (ClE_0=0x7ffff7b824c0)
    at /home/peter/.choosenim/toolchains/nim-2.0.8/lib/pure/asyncmacro.nim:33
#5  0x00005555555bc2b7 in _ZN13asyncdispatch23processPendingCallbacksE3refIN13asyncdispatch31PDispatcherBasecolonObjectType_EE3varI4boolE (p_p0=p_p0@entry=0x7ffff7b54120, didSomeWork_p1=didSomeWork_p1@entry=0x7fffffffd1bf)
    at /home/peter/.choosenim/toolchains/nim-2.0.8/lib/pure/asyncdispatch.nim:269
#6  0x00005555555bc5ac in _ZN13asyncdispatch7runOnceE3int (timeout_p0=timeout_p0@entry=500)
    at /home/peter/.choosenim/toolchains/nim-2.0.8/lib/pure/asyncdispatch.nim:1452
#7  0x00005555555bc94a in _ZN13asyncdispatch4pollE3int (timeout_p0=timeout_p0@entry=500)
    at /home/peter/.choosenim/toolchains/nim-2.0.8/lib/pure/asyncdispatch.nim:1711
#8  0x00005555555bfd9f in _ZN13asyncdispatch7waitForE6FutureI4voidE (fut_p0=fut_p0@entry=0x7ffff7b5a760)
    at /home/peter/.choosenim/toolchains/nim-2.0.8/lib/pure/asyncdispatch.nim:2022
#9  0x0000555555603287 in NimMainModule () at mycode.nim:112
```