operator== fails to compile if T is `void`

[Crzyrndm]

See https://godbolt.org/z/MvEoq4h7E

The std::expected docs for operator== cover this with the second overload I believe (T is void. No comparison is made against the "value")

[martinmoene]

Ah, thanks!
I have no memory of having noted this special case.
Will see to incorporating it, soon-ish.

Added, note to self:

• https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p0323r12.html#void
• https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p0323r12.html#expected.object.eq

[Crzyrndm]

From the second link above

• https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p0323r12.html#expected.void.eq

[martinmoene]

Add tests for operator==() with void 'value' type.

[Crzyrndm]

Just reviewing some old issues I created
This appears to be resolved in master (the godbolt example now works. Currently no release version created)