ci: set umask 022 to prevent group-writable cache dirs

ober

3f39ef668d73a0010aea3813c253e51e673b7709

diff --git a/.builds/ci.yml b/.builds/ci.yml
index 715e6c6..82f072f 100644
--- a/.builds/ci.yml
+++ b/.builds/ci.yml
@@ -14,6 +14,7 @@ sources:
 - https://git.sr.ht/~lisp/jerboa
 tasks:
 - build-and-test: |
+    umask 022
     cd jerboa
     sudo fallocate -l 4G /swapfile && sudo chmod 600 /swapfile && sudo mkswap /swapfile && sudo swapon /swapfile
     export CARGO_BUILD_JOBS=1