scalar-clone: add test coverage

scalar-clone: add test coverage

Create a new test file ('t9211-scalar-clone.sh') to exercise the options and
behavior of the 'scalar clone' command. Each test clones to a unique target
location and cleans up the cloned repo only when the test passes. This
ensures that failed tests' artifacts are captured in CI artifacts for
further debugging.

Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>