build(deps): bump golang from 1.25-alpine to 1.26-alpine in /docker/prod

Bumps golang from 1.25-alpine to 1.26-alpine.

---
updated-dependencies:
- dependency-name: golang
  dependency-version: 1.26-alpine
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docker/prod/Dockerfile

@@ -1,7 +1,7 @@
 # Set also `ARCH` ARG here so we can use it on all the `FROM`s. 
 ARG ARCH
 
-FROM golang:1.25-alpine as build-stage
+FROM golang:1.26-alpine as build-stage
 
 LABEL org.opencontainers.image.source=https://github.com/slok/sloth