Bump the dev-dependencies group with 2 updates

Bumps the dev-dependencies group with 2 updates: golang and alpine.


Updates `golang` from 1.20 to 1.21

Updates `alpine` from 3.18.2 to 3.18.4

---
updated-dependencies:
- dependency-name: golang
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: dev-dependencies
- dependency-name: alpine
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dev-dependencies
...

Signed-off-by: dependabot[bot] <[email protected]>

Dockerfile

@@ -1,5 +1,5 @@
 # Build the manager binary
-FROM golang:1.20 as builder
+FROM golang:1.21 as builder
 
 WORKDIR /workspace
 # Copy the Go Modules manifests
@@ -18,7 +18,7 @@ COPY lang/ lang/
 # Build
 RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -a -o manager main.go
 
-FROM alpine:3.18.2
+FROM alpine:3.18.4
 RUN apk add gpg gpg-agent
 WORKDIR /
 COPY --from=builder /workspace/manager .