ci: Use correct helper image even if both are built simultaneously

[mqasimsarfraz]

Currently, if both helper images are built together one of the images will have a default value since we set tag for both the images in each matric run. This change ensures we only set the default value when needed and not in each matric run.

I mainly hit it when doing some testing on the fork as mentioned below. Also, it was always the dnstester which is affected since it is done building before ebpf-builder. Perhaps something that will happen rarely in main repo but still a weird issue.

Fixes: 5ddb3fb

Testing done

w/o the change

• Run with both images built together can be found here. You can see the integration test are still using default dnstester image even if it was expected to use custom built image. The ebpf-builder still uses the correct custom image.

with the change

• Run with both images built together can be found here. You can see it is using custom image for both (ebpf-builder, dnstester the cases correctly.

[eiffel-fl]

Hi!

I understand the problem and you are indeed tackling it, but we do not need two steps for this, see my comment.
Also can you please check the commit message.

Best regards.

[eiffel-fl]

Looks good from CI point of view! Thank you for the fix!

[mqasimsarfraz]

Thanks for the review!