Update README.md for external-auth Test 4

[zhucebuliaolongchuan]

Title for Test 4 should be secure service with valid auth header. The current one is the same as Test 3.

What this PR does / why we need it:
There might be a typo for the title of the test that confuses somebody.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): None

Special notes for your reviewer:
None

/assign @aledbf

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[k8s-ci-robot]

Hi @zhucebuliaolongchuan. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[aledbf]

/ok-to-test

[codecov-io]

Codecov Report

Merging #4132 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4132      +/-   ##
==========================================
- Coverage   57.76%   57.74%   -0.02%     
==========================================
  Files          87       87              
  Lines        6459     6459              
==========================================
- Hits         3731     3730       -1     
- Misses       2296     2298       +2     
+ Partials      432      431       -1

Impacted Files	Coverage Δ
internal/watch/file_watcher.go	80.76% <0%> (-3.85%)	⬇️

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[aledbf]

/lgtm
/approve

[aledbf]

@zhucebuliaolongchuan thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, zhucebuliaolongchuan

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