fallback shell should not error when dynamic due to params access even with dynamic = "error"

[gnoff]

When producing a fallback shell params is dynamic. Normally anything dynamic shoudl be a build error when export const dynamic = "error" is used. however for fallback shells we'll never have fully static shells, nor should we since the whole point is to produce a PPR shell that server a wide range of paths. In the refactor for async dynamic APIs I introduced a bug where fallback param dynamic also errored if export const dynamic = "error" was used. This change corrects this behavior and adds a corresponding test

[ijjk]

Tests Passed