build(deps): bump fenix from b7bd932 to 6012e54

Bumps [fenix](https://github.com/nix-community/fenix) from `b7bd932` to `6012e54`.
- [Commits](nix-community/fenix@b7bd932...6012e54)

---
updated-dependencies:
- dependency-name: fenix
  dependency-version: 6012e5463531342033571efe294ec880bf13dd95
  dependency-type: direct:production
...

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

Author: dependabot[bot]