Cirrus: Fix git config permission denied

The buildah bud tests run rootless, so attempting to bypass the
ident-check with a `git config --system` fails with a permission denied
error (as it should).  Update the command to use `--global` instead,
which writes to `~/.gitconfig` and so works for regular users.

Also setup a fake identity for the CI-user and enable shell-debugging
for the commands to inform humans of what is happening in the script.

Signed-off-by: Chris Evich <cevich@redhat.com>

test/buildah-bud/run-buildah-bud-tests

@@ -155,7 +155,13 @@ if [[ -n $do_checkout ]]; then
     # under automation, nobody cares about this condition or message, because
     # the environment is disposable.
     if [[ "$CI" == "true" ]]; then
-      git config --system --add safe.directory $buildah_dir
+        (
+        _gc='git config --global'
+        set -x
+        $_gc user.email "TMcTestFace@example.com"
+        $_gc user.name "Testy McTestface"
+        $_gc --add safe.directory $buildah_dir
+        )
     fi
 
     cd $buildah_dir