Fix vault sync env continuation

[assistant-ngalaiko]

Summary

• move the assistant-vault-sync cacert comment out of the backslash-continued env command
• keep the certificate and vault variables in the same env invocation as supercronic

Validation

• nix fmt -- --fail-on-change
• nix flake check --no-build
• git diff --check

Follow-up to closed PR #48: the shell-continuation issue is still present on current master.