auspice/_config.yml: exclude "vendor/"

GitHub Action ruby/setup-ruby does not allow customization of the vendor
path¹ so just exclude the hard-coded `vendor/` path in the config.

¹ ruby/setup-ruby#136

Author: joverlee521

auspice/_config.yml

@@ -23,3 +23,4 @@ exclude:
   - "analysis/"
   - "aero-deploy.tar.gz"
   - "aero-debug.log"
+  - "vendor/"