Fix exposure of date, time and datetime object when threaded=True

[marvin-w]

Description

I assume that the second event loop in the connection thread was executed before the
tasks in the task registry were registered. And probably for some reason the currently running event loop
was the one from the connection thread. Since the event loop had already been started with run_forever() no new
tasks would be scheduled.

Fixes home-assistant/core#69328

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have performed a self-review of my own code
• The documentation has been adjusted accordingly
• The changes generate no new warnings
• Tests have been added that prove the fix is effective or that the feature works
• The changes are documented in the changelog
• The Homeassistant plugin has been adjusted in case of new config options

[codecov]

Codecov Report

Merging #925 (447e268) into main (28429ee) will decrease coverage by 0.00%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##             main     #925      +/-   ##
==========================================
- Coverage   95.56%   95.55%   -0.01%     
==========================================
  Files         130      130              
  Lines        7803     7810       +7     
==========================================
+ Hits         7457     7463       +6     
- Misses        346      347       +1     

Impacted Files	Coverage Δ
xknx/core/task_registry.py	98.43% <85.71%> (-1.57%)	⬇️
xknx/xknx.py	89.00% <100.00%> (+0.11%)	⬆️