Update on-cluster build docs to use Tekton 1.6.0

[creydr]

Tekton images have been moved from gcr.io to ghcr.io (see tektoncd/pipeline#8870). Using the old manifests leads failing image pulls nowadays. Therefore updating to the latest Tekton manifests.

[knative-prow]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.82%. Comparing base (b039190) to head (8a776ce).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3194      +/-   ##
==========================================
+ Coverage   51.81%   51.82%   +0.01%     
==========================================
  Files         162      162              
  Lines       19131    19131              
==========================================
+ Hits         9912     9914       +2     
+ Misses       8241     8240       -1     
+ Partials      978      977       -1     

Flag	Coverage Δ
integration	17.90% <ø> (+0.01%)	⬆️
unit macos-14	44.37% <ø> (ø)
unit macos-latest	44.37% <ø> (ø)
unit ubuntu-24.04-arm	44.56% <ø> (ø)
unit ubuntu-latest	45.31% <ø> (ø)
unit windows-latest	44.39% <ø> (ø)

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[creydr]

/hold
I see some pod affinity issues

[gauron99]

very strange 'reset by peer' errors across PRs currently

on top of some 'no space left on device' suddently

[lkingland]

Maybe reabase on main to get the updated test suite which is more aggressive about clearing disk space.