selftests: Make scripts executable

Fixes: 87b2d440 ("selftests: add memfd/sealing page-pinning tests")
Fixes: 2bf9e0ab ("locking/static_keys: Provide a selftest")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>