Set tests global git configuration for pull and merge to ff=only

Author: spog

test/00-git-config.t

@@ -15,6 +15,8 @@ git config --global user.name "Your Name"
 git config --global init.defaultBranch "master"
 git config --global --add safe.directory "$(pwd)"
 git config --global --add safe.directory "$(pwd)/.git"
+git config --global pull.ff only
+git config --global merge.ff only
 git config --list
 
 test-exists "${HOME}/.gitconfig"