fix(bundler): use BUNDLE_JOBS in `bi` to avoid config file change

When calling `bundle install` with `--jobs=<n>`, bundle persists this
argument in `.bundle/config`. If we run `BUNDLE_JOBS=<n> bundle install`
instead, this is not persisted.

Fixes #10425

plugins/bundler/bundler.plugin.zsh

@@ -40,7 +40,7 @@ bundle_install() {
   else
     local cores_num="$(nproc)"
   fi
-  bundle install --jobs="$cores_num" "$@"
+  BUNDLE_JOBS="$cores_num" bundle install "$@"
 }
 
 ## Gem wrapper