Bump golang from 1.20.7-alpine to 1.21.0-alpine (#32)

Bumps golang from 1.20.7-alpine to 1.21.0-alpine.

---
updated-dependencies:
- dependency-name: golang
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.20.7-alpine AS builder
+FROM golang:1.21.0-alpine AS builder
 WORKDIR /go/src/github.com/ingmarstein/mielesolar/
 COPY . .
 RUN apk add -U --no-cache ca-certificates git \