Bump chainguard-dev/apko from 0.27.0 to 0.28.0

Bumps [chainguard-dev/apko](https://github.com/chainguard-dev/terraform-provider-apko) from 0.27.0 to 0.28.0.
- [Release notes](https://github.com/chainguard-dev/terraform-provider-apko/releases)
- [Changelog](https://github.com/chainguard-dev/terraform-provider-apko/blob/main/.goreleaser.yml)
- [Commits](chainguard-dev/terraform-provider-apko@v0.27.0...v0.28.0)

---
updated-dependencies:
- dependency-name: chainguard-dev/apko
  dependency-version: 0.28.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

main.tf

@@ -6,7 +6,7 @@ terraform {
     }
     apko = {
       source  = "chainguard-dev/apko"
-      version = "0.27.0"
+      version = "0.28.0"
     }
     oci = {
       source  = "chainguard-dev/oci"