fix: prevent long handles from causing misalignment in add users modal

[V-Gira]

Description

Long user handles break the alignment of participants in the add users modal.
It appears flexbox is not computing the width of the truncated string correctly, even with the usual fix of assigning min-width: 0 to the wrapper div.
Assigning a width: 0 instead fixes the issue.

Screenshots/Screencast (for UI changes)

• min-width: 0
  

• width: 0
  

Checklist

• PR has been self reviewed by the author;
• Hard-to-understand areas of the code have been commented;
• If it is a core feature, unit tests have been added;

[codecov]

Codecov Report

Merging #15900 (46ac85d) into dev (82d43f8) will not change coverage.
The diff coverage is n/a.

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##              dev   #15900   +/-   ##
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  Coverage   44.53%   44.53%           
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  Files         674      674           
  Lines       22758    22758           
  Branches     5175     5175           
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  Hits        10136    10136           
  Misses      11325    11325           
  Partials     1297     1297