Previously, the http and https proxy agents used by actions were created based
on the protocol of the proxy URL itself - if the proxy was an http URL, both
the generated http and https agents supplied to axios were actually both
http proxy agents; if the proxy was an https URL, both the generated http and
https agents supplied to axios were both https proxy agents.
This PR changes so that both an http and https proxy agent are created and
assigned as the appropriate agents for axios. Similar changes were made to
the slack action, which does not directly use axios.
8fe204fcab