chore: update go.mod and vendor dependencies

[jflowers]

Description

Update go.mod to Go 1.26.7, add required dependencies for config tests, and generate vendor directory.

Acceptance Criteria

• go.mod updated: go 1.26.7
• Dependencies added:
  • github.com/ghodss/yaml
  • github.com/hmarr/codeowners
  • k8s.io/apimachinery
  • sigs.k8s.io/prow
• go.sum generated
• vendor/ directory generated via go mod vendor
• go mod tidy && go mod vendor && git diff --exit-code passes

References

• Modeled on: zero-dot-force/.github/go.mod