Bump golang from 1.20.7 to 1.21.0 (#175)

Bumps golang from 1.20.7 to 1.21.0.

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

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

Author: dependabot[bot]

Dockerfile

@@ -1,5 +1,5 @@
 # Build the manager binary
-FROM --platform=$BUILDPLATFORM golang:1.20.7 as builder
+FROM --platform=$BUILDPLATFORM golang:1.21.0 as builder
 
 ARG GOARCH=''
 ARG GITHUB_PAT=''