fix: Don't attempt to resolve artifacts if task is going to be skipped

[simster7]

Fixes: #2167

If – once parameter resolution has been done – we determine that the task will not run, do not attempt to resolve artifacts.

[codecov]

Codecov Report

Merging #2657 into master will increase coverage by 0.06%.
The diff coverage is 32.00%.

@@            Coverage Diff             @@
##           master    #2657      +/-   ##
==========================================
+ Coverage   11.16%   11.22%   +0.06%     
==========================================
  Files          83       83              
  Lines       32675    32696      +21     
==========================================
+ Hits         3648     3671      +23     
+ Misses      28529    28525       -4     
- Partials      498      500       +2     

Impacted Files	Coverage Δ
pkg/apis/workflow/v1alpha1/workflow_types.go	10.78% <0.00%> (-0.12%)	⬇️
server/workflow/workflow_server.go	35.84% <0.00%> (ø)
workflow/controller/operator.go	61.04% <0.00%> (ø)
workflow/controller/dag.go	55.12% <37.50%> (+4.50%)	⬆️
workflow/controller/steps.go	63.38% <45.45%> (-0.60%)	⬇️

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[simster7]

Back-ported to 2.7