flake: bump nixpkgs from `6b5e5b7` to `b47ad65`

Bumps [nixpkgs](https://github.com/NixOS/nixpkgs) from `6b5e5b7` to `b47ad65`.
- [Commits](https://github.com/NixOS/nixpkgs/compare/6b5e5b7a6631f065bf6908986990b37d845f847f...b47ad65d73ab65ded9ab408fe558866d71defee8)

---
updated-dependencies:
- dependency-name: nixpkgs
  dependency-version: b47ad65d73ab65ded9ab408fe558866d71defee8
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>