note the following log - without -X, you wouldn't know that the problem was that the extension was not found
I cannot actually tell what you ran to get this, or what the POM looks like to test it.
see attached POM.
[INFO] Error retrieving previous build number for artifact 'test:MNG-3650:jar': repository metadata for: 'snapshot test:MNG-3650:1.0-SNAPSHOT' could not be retrieved from repository: releases due to an error: Unsupported Protocol: 'foo': Cannot find wagon which supports the requested protocol: foo
Not great, but the error is there at the end.
Internal error in the plugin manager executing goal 'org.apache.maven.plugins:maven-deploy-plugin:2.3:deploy': Mojo execution failed.