euler_angles_ordered returns surprising results on gimbal lock (strange sign)

Consider the following example:

```rust
Rotation3::from_euler_angles(0., -90f64.to_radians(), 45f64.to_radians())
.euler_angles_ordered(
[
UnitVector3::new_normalize(Vector3::z()),
UnitVector3::new_normalize(Vector3::y()),
UnitVector3::new_normalize(Vector3::x()),
],
false,
)
```

The expected result is:

```rust
([0.7853981633974483, -1.5707963267948966, 0.0], false)
```

However, the actual result is:

```rust
([-0.7853981633974483, -1.5707963267948966, 0.0], false)
```

Notice the yaw sign is inverted.

Outside gimbal lock (so at pitch = -89.9 for example), the sign is as expected, so there's a weird discontinuity here.

At apex gimbal lock (so pitch = 90.0) the angle is also as expected.

It seems the yaw is multiplied redundantly by the sign of the pitch here.