test: avoid function name 'setup'

test: avoid function name 'setup'

pytest 7.3.2 treats the function name 'setup' as a fixture [1].

This leads to errors like:

    TypeError: setup() missing 2 required positional arguments:
    'disk_img' and 'osindications'

Rename setup() to capsule_setup().

[1] How to run tests written for nose
    https://docs.pytest.org/en/7.3.x/how-to/nose.html

Fixes: 482ef90aeb4c ("test: efi_capsule: refactor efi_capsule test")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>