ci: set umask 022 to prevent group-writable cache dirs (sr.ht default umask creates 0775 dirs)

ober

df3f1c9f6fe55ee55a307aa7bb46be7406f6bac6

diff --git a/.builds/ci.yml b/.builds/ci.yml
index f0646ca..82c0263 100644
--- a/.builds/ci.yml
+++ b/.builds/ci.yml
@@ -20,6 +20,7 @@ artifacts:
 - jerboa-signal/jerboa-signal-0.1.0.jpkg
 tasks:
 - build-jerboa: |
+    umask 022
     cd jerboa
     sudo fallocate -l 4G /swapfile && sudo chmod 600 /swapfile && sudo mkswap /swapfile && sudo swapon /swapfile
     export CARGO_BUILD_JOBS=1