Add 4GB swap + limit cargo to 1 job (avoid OOM on 2GB sr.ht VMs)

ober

a60ab419a0cb4917f71efc16b4d84629c9d5ccc7

diff --git a/.builds/ci.yml b/.builds/ci.yml
index 0cc297f..f5602a1 100644
--- a/.builds/ci.yml
+++ b/.builds/ci.yml
@@ -24,6 +24,8 @@ artifacts:
 tasks:
 - build-jerboa: |
     cd jerboa
+    sudo fallocate -l 4G /swapfile && sudo chmod 600 /swapfile && sudo mkswap /swapfile && sudo swapon /swapfile
+    export CARGO_BUILD_JOBS=1
     curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | \
       sh -s -- -y --profile minimal --default-toolchain 1.94.1
     source "$HOME/.cargo/env"