Swap to Environment Files (#360)

__test__/override-git-version.cmd

@@ -2,5 +2,5 @@
 mkdir override-git-version
 cd override-git-version
 echo @echo override git version 1.2.3 > git.cmd
-echo ::add-path::%CD%
+echo "%CD%" >> $GITHUB_PATH
 cd ..

__test__/override-git-version.sh

@@ -5,5 +5,5 @@ cd override-git-version
 echo "#!/bin/sh" > git
 echo "echo override git version 1.2.3" >> git
 chmod +x git
-echo "::add-path::$(pwd)"
+echo "$(pwd)" >> $GITHUB_PATH
 cd ..