Use rb_iseqw_to_iseq to get iseq pointer

[peterzhu2118]

Using DATA_PTR is internal implementation details so we should not use it.

It should fix this issue: ruby/ruby#10336 (comment)

[launchable-app]

Launchable Report

❌ Test session #2763453 failed   details on CI
_{🔔 no issues ✖️1 test failed ✔️63 tests passed}

❌ Test session #2763454 failed   details on CI
_{🔔 no issues ✖️1 test failed ✔️63 tests passed}

❌ Test session #2763485 failed   details on CI
_{🔔 no issues ✖️1 test failed ✔️63 tests passed}

❌ Test session #2763490 failed   details on CI
_{🔔 no issues ✖️1 test failed ✔️63 tests passed}

Passed test sessions

✅ Test session #2763443 passed   details on CI
✅ Test session #2763444 passed   details on CI
✅ Test session #2763445 passed   details on CI
✅ Test session #2763446 passed   details on CI
✅ Test session #2763447 passed   details on CI
✅ Test session #2763448 passed   details on CI
✅ Test session #2763449 passed   details on CI
✅ Test session #2763450 passed   details on CI
✅ Test session #2763451 passed   details on CI
✅ Test session #2763452 passed   details on CI
✅ Test session #2763455 passed   details on CI
✅ Test session #2763460 passed   details on CI
✅ Test session #2763461 passed   details on CI
✅ Test session #2763462 passed   details on CI
✅ Test session #2763463 passed   details on CI
✅ Test session #2763464 passed   details on CI
✅ Test session #2763465 passed   details on CI
✅ Test session #2763466 passed   details on CI
✅ Test session #2763467 passed   details on CI
✅ Test session #2763468 passed   details on CI
✅ Test session #2763548 passed   details on CI

Build: refs_pull_1093_merge_2d48ffe69ebebf712fe934309fc014e8b37d8959

[ko1]

Thanks!