Fix docstring and type hints for l_freq and h_freq in ICA.score_sources (#13689)

[DivyanshiJadon]

(Fixes #13689)

What does this implement/fix?

This PR makes two small, targeted changes in score_sources:

1. Function signature:

l_freq: float | None = None
h_freq: float | None = None
2.**Docstring:**
l_freq : float | None
    Low cut-off frequency. If None, no filtering is applied.
h_freq : float | None
    High cut-off frequency. If None, no filtering is applied.


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