fix(ci): disable kaniko cache for claudebox to fix DIGEST_INVALID

Corrupt cache blobs in rdev/claudebox/cache cause DIGEST_INVALID on
push. Disable cache temporarily to force a clean build. Can re-enable
once a good image is pushed and the cache is rebuilt.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.woodpecker.yml

@@ -57,7 +57,7 @@ steps:
         - ${CI_COMMIT_SHA:0:8}
       context: .
       dockerfile: Dockerfile
-      cache: true
+      cache: false
       skip_tls_verify: true
     when:
       <<: *when_main