assume localhost for the redis server

Author: ktoso

.github/workflows/pull_request.yml

@@ -18,6 +18,5 @@ jobs:
       linux_exclude_swift_versions: "[{\"swift_version\": \"5.8\"}]"
       # since we don't have systemctl, we run the redis server manually in the background
       linux_pre_build_command: apt-get update -y && apt-get install redis -y
-      linux_env_vars: REDIS_URL=redis
       linux_build_command: bash -c 'nohup redis-server & swift test'
       enable_windows_checks: false