Correct validators data in VEBO tests

[Psirex]

Here is an improved and corrected version of the text:

• In the tests for the validator exit bus, the commonly used getLastRequestedValidatorIndices() method does not handle cases where it returns -1. It is recommended to add an assert() to ensure that the returned value is not equal to -1. For instance, the check should be added in this example: test_veb_negative.py, Line 229.

• In some tests where a LidoValidator is created, an incorrect (validator_key, validator_id) pair is used. This can cause issues during test execution. An example of this can be found here: test_validator_exit_bus_happy_path.py, Line 86.