Fix test_image_spec

[pingsutw]

Tracking issue

https://github.com/flyteorg/flytekit/actions/runs/9475012693/job/26105636011

Why are the changes needed?

Unit test is failing

What changes were proposed in this pull request?

if image registry is localhost:30000, we should not use request to check if the image exists on docker hub

How was this patch tested?

unit test

Setup process

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

NA

Docs link

NA

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 44.54%. Comparing base (7ddfb9b) to head (a959720).
Report is 1 commits behind head on master.

Files	Patch %	Lines
flytekit/image_spec/image_spec.py	0.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2477       +/-   ##
===========================================
- Coverage   80.12%   44.54%   -35.59%     
===========================================
  Files         185      204       +19     
  Lines       18636    19584      +948     
  Branches     3853     3640      -213     
===========================================
- Hits        14933     8724     -6209     
- Misses       3056    10752     +7696     
+ Partials      647      108      -539     

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