src: remove unnecessary Isolate::GetCurrent() calls

These calls are unnecessary in Release mode but would still have
been included, so move them to the `DebugSealHandleScope` constructor.

PR-URL: https://github.com/nodejs/node/pull/33298


Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>