fix: closed review request "by (System)"

[IurmanJ]

Only display the user in the "Requested" column if it's a real human
(i.e., not "System").

Fix #3687

[codecov]

Codecov Report

Merging #4255 (0cc8842) into main (fe1f51a) will increase coverage by 0.01%.
The diff coverage is 96.96%.

@@            Coverage Diff             @@
##             main    #4255      +/-   ##
==========================================
+ Coverage   88.40%   88.41%   +0.01%     
==========================================
  Files         294      294              
  Lines       39197    39198       +1     
==========================================
+ Hits        34652    34657       +5     
+ Misses       4545     4541       -4     

Impacted Files	Coverage Δ
ietf/doc/urls.py	100.00% <ø> (ø)
ietf/utils/markdown.py	100.00% <ø> (ø)
ietf/doc/views_draft.py	91.98% <93.75%> (ø)
ietf/doc/views_ballot.py	91.86% <100.00%> (+0.10%)	⬆️
ietf/doc/views_doc.py	90.52% <100.00%> (+0.02%)	⬆️
ietf/doc/views_status_change.py	93.36% <100.00%> (+0.20%)	⬆️
ietf/utils/text.py	85.97% <100.00%> (+0.26%)	⬆️
ietf/submit/forms.py	82.88% <0.00%> (ø)
ietf/group/utils.py	94.59% <0.00%> (+0.90%)	⬆️

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