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

ober

e8a6ffbab3390230f02e9b7f023627501c89e63c

diff --git a/.build.yml b/.build.yml
index d48c939..b53e463 100644
--- a/.build.yml
+++ b/.build.yml
@@ -20,6 +20,8 @@ artifacts:
 tasks:
   - build-jerboa-tools: |
       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"