Fix unhandled asyncio.CancelledError during shutdown

[bachya]

Describe what the PR does:

SSIA

Does this fix a specific issue?

N/A

Checklist:

• Confirm that one or more new tests are written for the new functionality.
• Run tests and ensure everything passes (with 100% test coverage).
• Update README.md with any new documentation.

[codecov]

Codecov Report

Merging #766 (ccf3659) into dev (00dd5a4) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               dev      #766   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           31        31           
  Lines         1765      1758    -7     
=========================================
- Hits          1765      1758    -7     

Files	Coverage Δ
ecowitt2mqtt/runtime.py	100.00% <100.00%> (ø)