rust: document `bindgen` 0.71.0 regression

`bindgen` 0.71.0 regressed [1] on the "`--version` requires header"
issue which appeared in 0.69.0 first [2] and was fixed in 0.69.1. It
has been fixed again in 0.71.1 [3].

Thus document it so that, when we upgrade the minimum past 0.69.0 in the
future, we do not forget that we cannot remove the workaround until we
arrive at 0.71.1 at least.

Link: https://github.com/rust-lang/rust-bindgen/issues/3039 [1]
Link: https://github.com/rust-lang/rust-bindgen/issues/2677 [2]
Link: https://github.com/rust-lang/rust-bindgen/blob/main/CHANGELOG.md#v0711-2024-12-09

 [3]
Reviewed-by: Fiona Behrens <me@kloenk.dev>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20241209212544.1977065-1-ojeda@kernel.org


Signed-off-by: Miguel Ojeda <ojeda@kernel.org>