Fix segfault in cirrus CI

Author: sayantn

.cirrus.yml

@@ -2,6 +2,10 @@ task:
   name: x86_64-unknown-freebsd
   freebsd_instance:
     image_family: freebsd-13-4
+  env:
+    # FIXME(freebsd): FreeBSD has a segfault when `RUST_BACKTRACE` is set
+    # https://github.com/rust-lang/rust/issues/132185
+    RUST_BACKTRACE: "0"
   setup_script:
     - curl https://sh.rustup.rs -sSf --output rustup.sh
     - sh rustup.sh --default-toolchain nightly -y