build(deps): bump chainguard-dev/apko in /tflib/publisher

Bumps [chainguard-dev/apko](https://github.com/chainguard-dev/terraform-provider-apko) from 0.15.2 to 0.15.5.
- [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@v0.15.2...v0.15.5)

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

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

tflib/publisher/main.tf

@@ -6,7 +6,7 @@ terraform {
     }
     apko = {
       source  = "chainguard-dev/apko"
-      version = "0.15.2"
+      version = "0.15.5"
     }
     oci = {
       source  = "chainguard-dev/oci"