selftests/exec: binfmt_script: Add the overall result line according to TAP

The following line is missing from the test's execution. Add it to make
it fully TAP conformant:
# Totals: pass:27 fail:0 xfail:0 xpass:0 skip:0 error:0

Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240304155928.1818928-1-usama.anjum@collabora.com
Signed-off-by: Kees Cook <keescook@chromium.org>

selftests/exec: Rename file binfmt_script to binfmt_script.py

Rename file for readability purpose. Update its usage and references.

Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>