disable update test for istio

[dprotaso]

Istio update test is very flakey - part of #18

[knative-prow]

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[dprotaso]

/assign @izabelacg

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.93%. Comparing base (5fd30ff) to head (621e031).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #636   +/-   ##
=======================================
  Coverage   66.93%   66.93%           
=======================================
  Files          15       15           
  Lines         862      862           
=======================================
  Hits          577      577           
  Misses        254      254           
  Partials       31       31           

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[izabelacg]

/lgtm