I also tried that before and didn't work, I guess for some reason the erb compilation is not available at that point.

This is the error got:
  config/google_credentials.yml.erb): did not find expected key while parsing a block mapping at line 1 column 1

With the following content:
```yaml
development:
  google_key: ''
  google_secret: ''

test:
  google_key: ''
  google_secret: ''

 <%= IO.read("config/google_credentials.local.yml") if File.exists?("config/google_credentials.local.yml") %>
```