fix: Don't display Retry Nodes in UI if len(children) == 1

[simster7]

Fixes #2384. This new behavior reflects argo watch correctly.

Before:

After:

Behavior if len(children) > 1 is conserved:

[codecov]

Codecov Report

Merging #2390 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2390   +/-   ##
=======================================
  Coverage   13.13%   13.13%           
=======================================
  Files          72       72           
  Lines       25084    25084           
=======================================
  Hits         3294     3294           
  Misses      21375    21375           
  Partials      415      415

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