fix(ci): foo.com is no longer a bad gateway

[shreemaan-abhishek]

Description

foo.com used in traffic split test is a valid domain now and sending plain http request will yield 302 status code instead of 502.
https://github.com/apache/apisix/actions/runs/10823712557/job/30029684940?pr=11499#step:21:380

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[bzp2010]

Can we change that domain to something that can't possibly exist?
For example using a non-existent TLD like foo.local, which would not exist on any well known DNS, or even, we could leave the suffix alone.