fix: Specify UTC for TruncDate

[jennifer-richards]

Avoids mixing UTC and settings.TIME_ZONE in model_to_timeline_data()

[codecov]

Codecov Report

Merging #5996 (ea0802d) into main (09f3477) will decrease coverage by 0.04%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##             main    #5996      +/-   ##
==========================================
- Coverage   88.67%   88.63%   -0.04%     
==========================================
  Files         288      288              
  Lines       40001    40014      +13     
==========================================
- Hits        35471    35467       -4     
- Misses       4530     4547      +17     

Impacted Files	Coverage Δ
ietf/doc/views_stats.py	74.80% <ø> (ø)
ietf/ietfauth/widgets.py	84.61% <ø> (ø)
ietf/nomcom/views.py	92.90% <33.33%> (-0.22%)	⬇️
ietf/doc/utils.py	87.15% <100.00%> (+0.01%)	⬆️
ietf/nomcom/templatetags/nomcom_tags.py	70.83% <100.00%> (+3.64%)	⬆️
ietf/submit/forms.py	79.02% <100.00%> (+0.03%)	⬆️

... and 5 files with indirect coverage changes