chore(ci): bump Go toolchain to 1.26

[brentrager]

Problem

The Go toolchain was still pinned to 1.23.

Solution

One line in mise.toml: go = "1.23" → go = "1.26". Since the mise migration the toolchain version lives only there — CI uses jdx/mise-action@v4, and no workflow references a Go version.

Deliberately not touching the go directive in go/fetch/go.mod (still go 1.23.0). That declares the minimum language version for consumers of the published module; raising it would break anyone on an older toolchain.

Verification

Local, through mise on Go 1.26:

$ go version
go version go1.26.7 darwin/arm64
$ go build ./...        # OK
$ go vet ./...          # OK
$ go test ./...
ok  	github.com/SmooAI/fetch/go/fetch/v3	3.124s
$ gofmt -l .            # (no output)

No Go 1.26 incompatibilities found. pnpm format (oxfmt, which also formats .toml) leaves the diff unchanged.

🤖 Generated with Claude Code

https://claude.ai/code/session_013YaefW6U442PHZf94fMAer

[changeset-bot]

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