chore: bump minimum Go version to 1.25

[NickJosevski]

Why

The go directive has been pinned at 1.23.12 while every current consumer is already well ahead of it:

Consumer	go.mod
cli	1.26.6
octopus-argocd-gateway	1.26.0
terraform-provider-octopusdeploy	1.25.8

Because this is a public library, the go directive is the minimum version imposed on every consumer, so this stops short of the latest (1.27) deliberately — 1.25.0 clears the stale pin without forcing the Terraform provider to bump before it can take a new client release.

No dependency required this: the highest minimum across the module graph is go 1.23.0 (golang.org/x/text, net, crypto, sys).

The vet fallout

From language version 1.24 onward, vet's printf analyser reports non-constant format strings. That flags 43 jsonassert.Assertf call sites, which would fail the go vet -v ./... CI step:

non-constant format string in call to (*github.com/kinbiko/jsonassert.Asserter).Assertf

Each is fixed the same way:

-jsonassert.New(t).Assertf(expectedJSON, string(anonymousAsJSON))
+jsonassert.New(t).Assertf(expectedJSON, "%s", string(anonymousAsJSON))

This is behaviour-preserving. Assertf does fmt.Sprintf(expectedJSON, fmtArgs...) unconditionally, so with no args and no % in the string the result is identical — and strictly safer if serialised JSON ever contains a %. All 43 are in _test.go files; no production code is affected.

CI

Pinned to an explicit 1.27.x instead of >=1.19.0, which silently tracked whatever was newest — that's how a toolchain bump surprises you rather than being a deliberate change. Also bumps actions/setup-go v3 → v5.

Verification

• go build -race ./... — clean
• go vet ./... — clean under both go1.26.3 and go1.27.0 (the two toolchains flag slightly different subsets; the fix covers the union)
• gofmt -l — clean
• All 43 affected marshalling tests pass
• go mod tidy produces no go.sum churn

Note: unit and integration tests aren't separated in this repo, so a full local go test ./... can't pass without a live Octopus instance. The integration suite needs a CI run to confirm.

🤖 Generated with Claude Code