Update s2n

What's Changed

• Update phpunit for security fixes by @graebm in #61
• Fix it so CI runs on branches with '/' in name by @graebm in #62
• fix win build by @TingDaoK in #72
• Update s2n by @waahm7 in #81

New Contributors

• @graebm made their first contribution in #61
• @TingDaoK made their first contribution in #72
• @waahm7 made their first contribution in #81

Full Changelog: v1.0.2...v1.0.3