Make the poll tests resilient against signals
Make the poll tests resilient against signals

When run in Cirrus-CI's environment, the tests generate copious SIGRT_1
signals.  This commit ensures that the poll tests will retry on EINTR.

carllerche/nix-rust,nix-rust/nix,geofft/nix-rust,asomers/nix,carllerche/nix-rust,nix-rust/nix,geofft/nix-rust,asomers/nix,carllerche/nix-rust,geofft/nix-rust