X-Redirect-By type incomplete

[kkmuffme]

Setting the type to false (or any non-string) value, will disable sending the header.

I suggest adding false as type to document this behavior to make clear that false can be passed to NOT set this header.

[swissspidy]

Introduced in #42313

As much as I'd wish we don't need this and simply cast this to a string, it looks like some plugins are relying on this existing, yet undocumented, behavior.

[kkmuffme]

I'm definitely in favor of keeping this, as removing it with false is a use case that comes in handy in various cases, I just wanted to correct the type annotation.

[swissspidy]

In 57693:

Docs: Improve docblock for $x_redirect_by param in wp_redirect().

The $x_redirect_by parameter is supported by wp_redirect() and wp_safe_redirect() to set the X-Redirect-By header.
It can be modified via the x_redirect_by filter.

This updates the docblock to clarify that false can be passed to disable sending the header, which was previously undocumented behavior.

Props kkmuffme, swissspidy.
Fixes #60209.