Possibly fix an infinite recursion crash by avoid str() inside repr()

[matthiask]

See https://code.djangoproject.com/ticket/33134

[codecov]

Codecov Report

Merging #1507 (c53d48f) into main (d779328) will increase coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1507      +/-   ##
==========================================
+ Coverage   86.31%   86.47%   +0.15%     
==========================================
  Files          35       35              
  Lines        1893     1893              
  Branches      276      276              
==========================================
+ Hits         1634     1637       +3     
+ Misses        183      180       -3     
  Partials       76       76              

Impacted Files	Coverage Δ
debug_toolbar/panels/templates/panel.py	89.51% <0.00%> (+2.41%)	⬆️

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[tim-schilling]

Good catch.