Fix empty proxy-timeout failure

[xxx7xxxx]

In my last test case, there is always the annotation easegress.ingress.kubernetes.io/proxy-timeout, so it didn't fail. But it will fail if there isn't. It may fix the issue #1215 and #1235

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.63%. Comparing base (907f3f5) to head (83addd0).
Report is 2 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1236      +/-   ##
==========================================
+ Coverage   79.62%   79.63%   +0.01%     
==========================================
  Files         152      152              
  Lines       17228    17228              
==========================================
+ Hits        13718    13720       +2     
+ Misses       2847     2845       -2     
  Partials      663      663              

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