Update num-bigint requirement from 0.2 to 0.3

Updates the requirements on [num-bigint](https://github.com/rust-num/num-bigint) to permit the latest version.
- [Release notes](https://github.com/rust-num/num-bigint/releases)
- [Changelog](https://github.com/rust-num/num-bigint/blob/master/RELEASES.md)
- [Commits](rust-num/num-bigint@num-bigint-0.2.0...num-bigint-0.3.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Cargo.toml

@@ -23,7 +23,7 @@ indoc = { version = "0.3.4", optional = true }
 inventory = { version = "0.1.4", optional = true }
 libc = "0.2.62"
 parking_lot = "0.10.2"
-num-bigint = { version = "0.2", optional = true }
+num-bigint = { version = "0.3", optional = true }
 num-complex = { version = "0.2", optional = true }
 paste = { version = "0.1.6", optional = true }
 pyo3cls = { path = "pyo3cls", version = "=0.10.1", optional = true }