Handle requests.exceptions.SSLError in manager._slack_notification()

[douglatornell]

An unhandled requests.exceptions.SSLError exception in manager._slack_notification() caused the SalishSeaNowcast
manager to crash and restart in such a way that processing didn't continue and completed collect_weather and crop_gribs workers were left running.

We should catch the exception and emit an ERROR level log message so that processing continues but automation administrators are notified by email.

Traceback (most recent call last):
  File "/SalishSeaCast/NEMO_Nowcast/nemo_nowcast/manager.py", line 267, in _process_messages
    self._try_messages()
  File "/SalishSeaCast/NEMO_Nowcast/nemo_nowcast/manager.py", line 287, in _try_messages
    reply, next_workers = self._message_handler(message)
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/SalishSeaCast/NEMO_Nowcast/nemo_nowcast/manager.py", line 309, in _message_handler
    reply, next_workers = self._handle_continue_msg(msg)
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/SalishSeaCast/NEMO_Nowcast/nemo_nowcast/manager.py", line 357, in _handle_continue_msg
    self._slack_notification(msg)
  File "/SalishSeaCast/NEMO_Nowcast/nemo_nowcast/manager.py", line 467, in _slack_notification
    requests.post(slack_url, json=slack_msg)
  File "/SalishSeaCast/nowcast-env/lib/python3.12/site-packages/requests/api.py", line 115, in post
    return request("post", url, data=data, json=json, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/SalishSeaCast/nowcast-env/lib/python3.12/site-packages/requests/api.py", line 59, in request
    return session.request(method=method, url=url, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/SalishSeaCast/nowcast-env/lib/python3.12/site-packages/requests/sessions.py", line 589, in request
    resp = self.send(prep, **send_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/SalishSeaCast/nowcast-env/lib/python3.12/site-packages/requests/sessions.py", line 703, in send
    r = adapter.send(request, **kwargs)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/SalishSeaCast/nowcast-env/lib/python3.12/site-packages/requests/adapters.py", line 698, in send
    raise SSLError(e, request=request)
requests.exceptions.SSLError: HTTPSConnectionPool(host='hooks.slack.com', port=443): Max retries exceeded with url: /services/TFR25L4LU/BFXM1R6AK/qJyGMDo9KPEXIwJob0SwuxD3 (Caused by SSLError(SSLEOFError(8, '[SSL: UNEXPECTED_EOF_WHILE_READING] EOF occurred in violation of protocol (_ssl.c:1000)')))