Bump golang from 1.21.4-alpine3.18 to 1.21.5-alpine3.18

Bumps golang from 1.21.4-alpine3.18 to 1.21.5-alpine3.18.

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

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

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.21.4-alpine3.18 AS builder
+FROM golang:1.21.5-alpine3.18 AS builder
 WORKDIR /go/src/github.com/mrueg/netcupscp-exporter
 COPY . .
 RUN apk --no-cache add make git && make