Fix rb_eSystemExit raised in Ractor

[Bug #21505]

Previously `Ractor.new { exit }.join` would hang because SystemExit was
special cased.

This commit updates this to take the same path as other exceptions,
which wraps the exception in a Ractor::RemoteError and does not end up
exiting the main Ractor. I don't know if that's what this should do, but
I think it's a reasonable behaviour as calling exit() in a Ractor is
odd.

    in 'Ractor#join': thrown by remote Ractor. (Ractor::RemoteError)
       from -e:1:in '<main>'
    in 'Kernel#exit': exit (SystemExit)
            from -e:1:in 'block in <main>'

0 files changed, 0 insertions, 0 deletions