t0003: move setup for `--all` into new block

t0003: move setup for `--all` into new block

There is some setup code which is used by multiple tests being setup in
`attribute test: --all option`. This means when we run "sh
./t0003-attributes.sh --run=setup,<num>" there is a chance of failing
since we missed this setup block.

So to ensure that setups are independent of test logic, move this to a
new setup block.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Co-authored-by: toon@iotcl.com
Signed-off-by: Junio C Hamano <gitster@pobox.com>