fix: Fix some HTML validation errors that came in via #4035

[larseggert]

Also make validation errors display a bit better.

[codecov]

Codecov Report

Merging #4066 (cbcbb76) into main (8b6dbf3) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head cbcbb76 differs from pull request most recent head 72c2947. Consider uploading reports for the commit 72c2947 to get more accurate results

@@            Coverage Diff             @@
##             main    #4066      +/-   ##
==========================================
- Coverage   88.14%   88.14%   -0.01%     
==========================================
  Files         297      297              
  Lines       39275    39275              
==========================================
- Hits        34620    34618       -2     
- Misses       4655     4657       +2     

Impacted Files	Coverage Δ
ietf/urls.py	81.08% <ø> (ø)
ietf/utils/pipe.py	82.60% <0.00%> (-4.35%)	⬇️
ietf/submit/forms.py	82.92% <0.00%> (-0.23%)	⬇️

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