deconflict variable for action and each block

[tanhauhau]

Fixes #5834

Before submitting the PR, please make sure you do the following

- [ ] It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs

• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with npm test and lint the project with npm run lint

[Conduitry]

I'm seeing compiler exceptions of TypeError: Cannot read property 'template_scope' of null during several of the tests.