Describe the bug
After #2936, when I build the release yamls using ./hack/release.sh --skip-tests, I don't see config-br-default-channel and config-br-defaults in the release manifest `eventing.yaml.

Expected behavior
Default broker config to be included in the release manifest, eventing.yaml.

Contents of these 2 files should be in the output:

• 400-config-br-default-channel.yaml
• 400-config-br-defaults.yaml.

To Reproduce
Do ./hack/release.sh --skip-tests, check the resulting eventing.yaml file.

Knative release version
0.13

Additional context
Basically the comment: #2936 (comment)