selftests: drv-net: psp: fix templated test names in psp_ip_ver_test_builder()

selftests: drv-net: psp: fix templated test names in psp_ip_ver_test_builder()

test_case will only take on its formatted name after it is called by
the test runner. Move the assignment to test_case.__name__ to when the
test_case is constructed, not called.

Fixes: 8f90dc6e417a ("selftests: drv-net: psp: add basic data transfer and key rotation tests")
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
Link: https://patch.msgid.link/20251216-psp-test-fix-v1-1-3b5a6dde186f@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>