ci: remove unmaintained upgrade-go workflow

[xavpaice]

Description, Motivation and Context

Removes the Upgrade Go Version workflow (.github/workflows/upgrade-go.yaml).

The workflow relied on StefMa/Upgrade-Go-Action@v1, which currently targets Node 20. GitHub has deprecated Node 20 on Actions runners, causing deprecation warnings on every run (e.g. run 30799850499).

The upstream project is not well maintained: the v1 tag still points to the initial v1.0.0 release from December 2024, and no new release has been cut with the Node 24 fix that exists on main. Pinning the action to @main for a workflow that opens automated PRs is not desirable, so we are removing the automation instead.

There is no official GitHub action for updating the Go toolchain version in go.mod. Dependabot is already configured in this repo for Go module dependencies and GitHub Actions updates, but it does not bump the go directive itself. Go version upgrades will be handled manually going forward.

Checklist

• New and existing tests pass locally with introduced changes.
• Tests for the changes have been added (for bug fixes / features)
• The commit message(s) are informative and highlight any breaking changes
• Any documentation required has been added/updated. For changes to https://troubleshoot.sh/ create a PR here

Does this PR introduce a breaking change?

• Yes
• No

[greptile-apps]

_{Reviews (1): Last reviewed commit: "ci: remove unmaintained upgrade-go workf..." | Re-trigger Greptile}