feat: improve the e2e test of referer-restriction plugin

[Chever-John]

The original e2e testing of the referer-restriction plugin was not perfect, and the purpose of this PR is to improve the testing of the plugin.

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What this PR does / why we need it:

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[codecov-commenter]

Codecov Report

Merging #976 (b433ce3) into master (0f4391a) will not change coverage.
The diff coverage is n/a.

❗ Current head b433ce3 differs from pull request most recent head f971dfa. Consider uploading reports for the commit f971dfa to get more accurate results

@@           Coverage Diff           @@
##           master     #976   +/-   ##
=======================================
  Coverage   31.91%   31.91%           
=======================================
  Files          73       73           
  Lines        7953     7953           
=======================================
  Hits         2538     2538           
  Misses       5139     5139           
  Partials      276      276           

Impacted Files	Coverage Δ
pkg/api/router/apisix_healthz.go	66.66% <ø> (ø)

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[tao12345666333]

thanks, can you add a case for check the message?

[Chever-John]

thanks, can you add a case for check the message?

have finished it~

[jwrookie]

LGTM

[tao12345666333]

LGTM

Thanks