Figure.text: Fix warning for font parameter

[yvonnefroehlich]

Description of proposed changes

I am wondering about the context of the type bool for the angle and font parameters of Figure.text.

    angle: float | Sequence[float] | bool = False,
    font: str | StringArrayTypes | bool = False,

Why was there a change from None to False in PR #4489? I believe this causes the newly occuring warning by the Figure.text method, e.g., https://www.pygmt.org/dev/tutorials/basics/text.html:

text [WARNING]: Length <unit> e not supported - revert to default unit [point]
text [WARNING]: Fals not a valid number and may not be decoded properly.
text [WARNING]: Representation of font size not recognized. Using default.

When changing back to None the warning does no longer occur.

Preview: https://pygmt-dev--4576.org.readthedocs.build/en/4576/gallery/embellishments/text_formatting.html

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[yvonnefroehlich]

Superseded by PR #4577.