fix: Let csv.writer handle encoding for agenda_csv view

[jennifer-richards]

Fixes #5224

[codecov]

Codecov Report

Merging #5225 (8987f0a) into main (0ec1264) will decrease coverage by 0.03%.
The diff coverage is 90.69%.

@@            Coverage Diff             @@
##             main    #5225      +/-   ##
==========================================
- Coverage   88.58%   88.56%   -0.03%     
==========================================
  Files         295      294       -1     
  Lines       40114    40088      -26     
==========================================
- Hits        35534    35502      -32     
- Misses       4580     4586       +6     

Impacted Files	Coverage Δ
ietf/iesg/urls.py	100.00% <ø> (ø)
ietf/meeting/urls.py	81.25% <ø> (ø)
ietf/iesg/views.py	92.53% <85.18%> (-0.71%)	⬇️
ietf/doc/mails.py	96.20% <100.00%> (ø)
ietf/group/views.py	90.95% <100.00%> (+0.09%)	⬆️
ietf/meeting/helpers.py	89.84% <100.00%> (-0.07%)	⬇️
ietf/meeting/views.py	91.13% <100.00%> (+<0.01%)	⬆️
ietf/secr/proceedings/proc_utils.py	86.33% <100.00%> (ø)
ietf/utils/text.py	85.97% <0.00%> (-1.22%)	⬇️
ietf/doc/views_search.py	88.63% <0.00%> (-0.62%)	⬇️
... and 2 more

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