Update go toolchain directive to v1.26.5

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
go (source)	toolchain	patch	1.26.4 → 1.26.5

---

Release Notes

golang/go (go)

v1.26.5

---

Configuration

📅 Schedule: (in timezone Japan)

• Branch creation
  • "every weekend"
• Automerge
  • At any time (no schedule defined)

🚦 Automerge: Enabled.

♻ Rebasing: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

---

• If you want to rebase/retry this PR, check this box

---

This PR was generated by Mend Renovate. View the repository job log.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.49%. Comparing base (a1857ca) to head (1857246).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #300   +/-   ##
=======================================
  Coverage   44.49%   44.49%           
=======================================
  Files          15       15           
  Lines         636      636           
=======================================
  Hits          283      283           
  Misses        306      306           
  Partials       47       47           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.