chore(deps): update golang docker tag to v1.26 (#23)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| golang | stage | minor | `1.25` → `1.26` |

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Reviewed-on: #23
Co-authored-by: renovate[bot] <renovate-bot@git.tainton.uk>
Co-committed-by: renovate[bot] <renovate-bot@git.tainton.uk>

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.25 AS build
+FROM golang:1.26 AS build
 WORKDIR /src
 COPY go.mod ./
 RUN go mod download