Fix GH-16181: phpdbg: exit in exception handler reports fatal error

When running PHP code, we must not handle `UnwindExit` exceptions, but
rather have to ignore them.

Closes GH-

Fix GH-16181: phpdbg: exit in exception handler reports fatal error

When running PHP code, we must not handle `UnwindExit` exceptions, but
rather have to ignore them.

Closes GH-16182.

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