chore(deps): bump golang from 1.20.6-alpine to 1.21.0-alpine (#2604)

Bumps golang from 1.20.6-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.standalone

@@ -1,6 +1,6 @@
 # This version of Dockerfile is for building without external dependencies.
 # Build a multi-platform image e.g. `docker buildx build --push --platform linux/arm64,linux/amd64 --tag external-secrets:dev --file Dockerfile.standalone .`
-FROM golang:1.20.6-alpine AS builder
+FROM golang:1.21.0-alpine AS builder
 ARG TARGETOS
 ARG TARGETARCH
 ENV CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH}