Update Pipeline LTS versions

[github-actions]

Automated Pipeline LTS Update

This PR updates the Pipeline LTS versions used in e2e testing.

Updated versions:

[
  "v1.15.0",
  "v1.12.0",
  "v1.9.3",
  "v1.6.2",
  "v1.3.4"
]

Source: tektoncd/pipeline releases.md

---

🤖 This PR was automatically created by the Update Pipeline LTS versions workflow.

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[tekton-robot]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.95%. Comparing base (0548d01) to head (d3d9812).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1869      +/-   ##
==========================================
+ Coverage   61.90%   61.95%   +0.04%     
==========================================
  Files          64       64              
  Lines        4071     4071              
==========================================
+ Hits         2520     2522       +2     
+ Misses       1269     1268       -1     
+ Partials      282      281       -1     

Flag	Coverage Δ
unit-tests	61.95% <ø> (+0.04%)	⬆️

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