fix: sort higher capacity rooms first in schedule editor

[jennifer-richards]

In the meeting schedule editor, rooms were meant to be sorted in decreasing order of capacity (among other criteria). Due to a bug, they were actually sorted in increasing order. Oops.

This fixes that and also handles the case where capacity is None.

Partially addresses #4377 but there is probably further work to do there.

[codecov]

Codecov Report

Merging #4653 (981c3bf) into main (d34e88d) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #4653      +/-   ##
==========================================
- Coverage   88.43%   88.41%   -0.03%     
==========================================
  Files         296      296              
  Lines       39716    39730      +14     
==========================================
+ Hits        35122    35126       +4     
- Misses       4594     4604      +10     

Impacted Files	Coverage Δ
ietf/meeting/views.py	90.52% <ø> (ø)
ietf/utils/timezone.py	91.17% <100.00%> (+6.17%)	⬆️
ietf/doc/views_search.py	89.23% <0.00%> (-1.04%)	⬇️
ietf/group/utils.py	93.72% <0.00%> (-0.90%)	⬇️
ietf/utils/mail.py	79.62% <0.00%> (-0.47%)	⬇️
ietf/submit/forms.py	82.70% <0.00%> (-0.18%)	⬇️

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