build: bump Go to v1.26.7

[FengyuanYin]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Updates the Go version from 1.26.6 to 1.26.7 in go.mod and all Docker build images to keep the project toolchain consistent and up to date.

Which issue(s) this PR fixes:

NONE

Special notes for your reviewer:

The Go version has been updated consistently across go.mod and the three Dockerfiles.

Does this PR introduce a user-facing change?:

NONE

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.96%. Comparing base (5903457) to head (3df0903).
⚠️ Report is 5 commits behind head on main.
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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #458      +/-   ##
==========================================
- Coverage   59.98%   59.96%   -0.03%     
==========================================
  Files          36       36              
  Lines        3589     3589              
==========================================
- Hits         2153     2152       -1     
- Misses       1216     1218       +2     
+ Partials      220      219       -1     

Flag	Coverage Δ
unittests	59.96% <ø> (-0.03%)	⬇️

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[RainbowMango]

/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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