Do not rewrite timestamps.

This is to fix buildkit caching.

.webhook_bridge/pipeline-foreign-document-test.yaml

@@ -119,7 +119,7 @@ spec:
               - --import-cache
               - "type=registry,ref=$(params.image-name):buildcache"
               - --export-cache
-              - "type=registry,ref=$(params.image-name):buildcache,mode=max,compression=zstd,compression-level=22,rewrite-timestamp=true,image-manifest=true,oci-mediatypes=true"
+              - "type=registry,ref=$(params.image-name):buildcache,mode=max,compression=zstd,compression-level=22,image-manifest=true,oci-mediatypes=true"
               - --opt
               - build-arg:SOURCE_DATE_EPOCH=$(tasks.get-git-commit-time.results.unix-time)
           - name: BUILDKITD_TOML