work around another swig4 change

* python/spot/impl.i: Make sure spot::acc_cond::mark_t::operator<<
exceptions are not ignored.
13 jobs for next in 129 minutes and 24 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #47982
alpine-gcc

00:25:36

passed #47983
arch-clang

00:51:09

passed #47984
arch-gcc-glibcxxdebug

00:51:53

passed #47981
debian-gcc-snapshot

01:18:10

passed #47979
debian-stable-gcc

00:39:30

passed #47980
debian-unstable-gcc-coverage

01:14:15

88.7%
passed #47987
debpkg-stable

01:58:40

passed #47988
debpkg-unstable

01:58:01

passed #47985
mingw-shared

00:09:54

passed #47986
mingw-static

00:08:47

passed #47989
rpm-pkg

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  Publish
passed #47990
dput
publish-rpm

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passed #47991
dput
publish-unstable

00:02:23