Fix latest minor version issue in docker skip cilium upgrade E2E

[rahulbabu95]

Cilium Skip Upgrade tests fail when run against the release branch when the release isn't out already as it picks up the wrong latest minor version. Make the test to derive at the latest minor based on the test branch it is run against to rightly calculate the previous latest minor release.

Issue #, if available:

Description of changes:

Testing (if applicable):

Documentation added/planned (if applicable):

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ff55ac1) 71.96% compared to head (9b10bdd) 71.94%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6894      +/-   ##
==========================================
- Coverage   71.96%   71.94%   -0.02%     
==========================================
  Files         532      532              
  Lines       41601    41593       -8     
==========================================
- Hits        29938    29924      -14     
- Misses       9987     9991       +4     
- Partials     1676     1678       +2     

Files	Coverage Δ
controllers/cluster_controller.go	75.92% <100.00%> (-1.28%)	⬇️

... and 1 file with indirect coverage changes

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[ahreehong]

/retest

[rahulbabu95]

/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rahulbabu95

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[rahulbabu95]

/cherrypick release-0.18

[eks-distro-pr-bot]

@rahulbabu95: new pull request created: #6897

In response to this:

/cherrypick release-0.18

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