fix: Fix tree shaking even more (vercel/turbo#8864)
### Description
Fix server action and rename the injected variable.
The previous code fails if the name of the top-level variable is `v`.
This was not a problem for almost all modules, but some packages like
[`@firebase/webchannel-wrapper`](https://unpkg.com/@firebase/webchannel-wrapper@0.2.41/dist/index.esm.js)
is published after mangling, so it can be a problem
### Testing Instructions
See https://github.com/vercel/next.js/pull/66689
