Question

Why do I see the following warning?

$ git config --global http.proxy http://172.19.18.22:8080
warning: http.proxy has multiple values

Answer 1

Simple display all three configuration level (system, global and local) in order to check if you see several http.proxy configuration:

git config -l

You can then proceed to remove the extra one with a:

git config --system (or --global or --local) --unset http.proxy

liwp mentions in the comment a:

git config --system (or --global or --local) --unset-all http.proxy

to get of all http.proxy entries