github: always push via ssh

https://git-scm.com/docs/git-config#Documentation/git-config.txt-urlltbasegtpushInsteadOf

gitconfig

@@ -41,6 +41,9 @@
 [push]
 	default = simple
 
+[url "git@github.com:"]
+	pushInsteadOf = https://github.com/
+
 [tag]
 	forceSignAnnotated = true