chore(deps): bump Go and deps for CVE remediation

[infernus01]

Changes

Bump Go from 1.26.1 to 1.26.5 and update 3 indirect
dependencies.
Go stdlib (1.26.1 → 1.26.5):

• CVE-2026-39822 (Important) — os.Root symlink escape
• CVE-2026-42505 (Moderate) — crypto/tls ECH privacy leak
  Dependency bumps:
• github.com/sigstore/sigstore-go 1.1.4 → 1.2.1 (CVE-2026-49834)
• github.com/google/cel-go 0.28.1 → 0.29.2 (GHSA-gcjh-h69q-9w9g)
• github.com/go-chi/chi/v5 5.2.5 → 5.3.0 (GHSA-3fxj-6jh8-hvhx, GHSA-rjr7-jggh-pgcp, GHSA-9g5q-2w5x-hmxf)

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[infernus01]

/kind misc

[tekton-robot]

@infernus01: PR needs rebase.

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