Bump Go to 1.25.6

[Copilot]

Summary

Bumps Go from 1.25.5 to 1.25.6.

• Updated go.mod Go directive to 1.25.6
• Updated .github/workflows/test-s390x.yml to download Go 1.25.6 for s390x testing (was on 1.25.3)
• Updated acceptance/testdata/launcher/Dockerfile to use golang:1.25.6 (was on 1.25.3)

Other workflows using go-version-file: 'go.mod' automatically pick up the new version.

Release notes

Updates Go toolchain to 1.25.6.

---

Related

---

Context

Build verified across all supported architectures (amd64, arm64, ppc64le, s390x). The Dockerfile update ensures scanners and individuals won't misidentify the project as using an older Go version.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Bump go to 1.25.6</issue_title>
<issue_description>### Summary

Bump go minor version to 1.25.6

---

Proposal

• Bump go.mod
• Updated dockerfile
• Update .github/workflows/test-s390x.yml go reference.

---

Context

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Bump go to 1.25.6 #1588

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[jabrown85]

@copilot the Dockerfile here can also be bumped. Only so any scanners/individuals won't misidentify lifecycle as being on an older version by finding the string in the repo.

[Copilot]

@copilot the Dockerfile here can also be bumped. Only so any scanners/individuals won't misidentify `li...

Updated in commit 54625ab.