Use workspace lints to control unexpected_cfgs. (#682)

By using `workspace.lints`, we can configure lints once for
everything (and then inherit it into the various crates).

The lint configuration for `unexpected_cfgs` works in 1.80+
and warns otherwise.

Co-authored-by: Thierry Berger <contact@thierryberger.com>

crates/rapier_testbed3d/Cargo.toml

@@ -24,6 +24,9 @@ name = "rapier_testbed3d"
 path = "../../src_testbed/lib.rs"
 required-features = ["dim3"]
 
+[lints]
+workspace = true
+
 [features]
 default = ["dim3"]
 dim3 = []