Renamer stack-overflows on large test suites

When writing large test suites using the `test` stdlib, `Renamer` reaches a stack overflow. (With even larger test suites, doubling the number of tests in the example below, `Namer` will stack overflow.)

## Reproducing the issue

Test suite that triggers a stack overflow in `Renamer` for me:
``` effekt
import test

def main() = {
suite("Testsuite") {
test("A test") { assert(1,1) } // repeated 500 times
}
}
```
https://gist.github.com/marzipankaiser/407983d6cb012e11c03753afeb464bed

I have not, as of yet, managed to reproduce the issue with simplified higher-order functions (not from the test stdlib), but I would assume it's possible.

## Expected behavior
I would expect a long (not highly nested) program to compile normally.