fix: double go download buildpacks

[gauron99]

• ensure explicit go version is passed into buildpacks (from function's go.mod file)
  /fixes [go] func build installs go twice? #3178

[knative-prow]

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[codecov]

Codecov Report

❌ Patch coverage is 68.42105% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.37%. Comparing base (f508122) to head (6ffb3ae).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/buildpacks/builder.go	68.42%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3360      +/-   ##
==========================================
- Coverage   55.14%   53.37%   -1.78%     
==========================================
  Files         170      170              
  Lines       19970    19989      +19     
==========================================
- Hits        11013    10669     -344     
- Misses       7880     8293     +413     
+ Partials     1077     1027      -50     

Flag	Coverage Δ
e2e	37.78% <0.00%> (-1.63%)	⬇️
e2e go	?
e2e node	30.95% <0.00%> (-0.04%)	⬇️
e2e python	35.05% <0.00%> (-0.04%)	⬇️
e2e quarkus	31.09% <0.00%> (-0.04%)	⬇️
e2e rust	30.54% <0.00%> (-0.03%)	⬇️
e2e springboot	30.59% <0.00%> (-0.04%)	⬇️
e2e typescript	31.06% <0.00%> (-0.04%)	⬇️
integration	?
unit macos-14	45.13% <73.33%> (+0.02%)	⬆️
unit macos-latest	45.13% <73.33%> (+0.02%)	⬆️
unit ubuntu-24.04-arm	45.22% <68.42%> (+0.02%)	⬆️
unit ubuntu-latest	46.03% <73.33%> (+0.02%)	⬆️
unit windows-latest	45.15% <73.33%> (+0.02%)	⬆️

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[gauron99]

The problem here is that we need to identify "lowest supported version by bp"

[gauron99]

I think I have a fix

[gauron99]

fix now part of scaffolding #3237