fix[test]: fix test in grammar fuzzer

[charles-cooper]

What I did

fix a failing test run in https://github.com/vyperlang/vyper/actions/runs/9503241643/job/26193257852 (copy paste of the error below):

=========================== short test summary info ============================
FAILED tests/functional/grammar/test_grammar.py::test_grammar_bruteforce - IndexError: list index out of range
Falsifying example: test_grammar_bruteforce(
    code='"""\r""" \n""""""',
)

You can reproduce this example by temporarily adding @reproduce_failure('6.103.1', b'AXicY+RnYGD0BWJGRgY4AAAGWwBi') as a decorator on your test case
============ 1 failed, 734 passed, 8 warnings in 192.85s (0:03:12) =============
Error: Process completed with exit code 1.

How I did it

How to verify it

Commit message

hypothesis `6.103.1` generates examples like

```
Falsifying example: test_grammar_bruteforce(
    code='"""\r""" \n""""""',
)
```

which trivially raise an exception in asttokens. filter out `\r`
characters when generating source codes.

Description for the changelog

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