Bump bigdecimal & fix failing test

[cakebaker]

This PR bumps bigdecimal from 0.4.7 to 0.4.8 and fixes a failing test.

[RenjiSann]

@drinkcat If you want to take a look at the test fix

[drinkcat]

Thanks for tagging me! ,-)

Huh... 3 things:

1. The Display trait implementation is actually dead code, nothing uses it (apart from the unit test just below)...
2. When I was looking at it, I never really quite understood what was the intent of this line anyway: Self::BigDecimal(BigDecimal::new(n * 10, 1)).fmt(f), seems like an attempt to get a decimal point in all cases? But is this the right thing to do?
3. The failing test is inconsistent anyway: ::zero gets formatted as 0.0, but MinusZero as -0?

So... up to you. IMHO you could delete the implementation, or change the test to check for 0 instead.

If we keep the implementation, I'd remove that n*10,1 thing too (and just do Self::BigDecimal(x) => x.fmt(f)).

Oh, and a 4th thing ,-P You could grep for https://github.com/akubera/bigdecimal-rs/issues/144 in the code and remove the workaround and enable the tests as part of this (but I'm happy to do it if you don't have cycles!).

[cakebaker]

Changes since last push:

• removed Display implementation of ExtendedBigDecimal
• fixed TODOs related to https://github.com/akubera/bigdecimal-rs/issues/144 (thanks for the hint about them, @drinkcat)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[drinkcat]

LGTM thanks!