python312Packages.diffimg: fix test

[evils]

python 3.12 seems to yield a very slightly different result
change is the least significant digit of a ratio, seems safe

and upgrade to --replace-warn while i'm here

found via #291134 but shouldn't block it

affected line:
https://github.com/nicolashahn/diffimg/blob/b82f0bb416f100f9105ccccf1995872b29302461/diffimg/test.py#L80

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

---

Add a 👍 reaction to pull requests you find important.

[kirillrdy]

Result of nixpkgs-review pr 296323 run on x86_64-linux 1

5 packages failed to build:

• kicad-unstable
• kicad-unstable-small
• python312Packages.kicad
• python312Packages.pcbnew-transition
• python312Packages.pcbnew-transition.dist

19 packages built:

• kicad
• kicad-small
• kicad-testing
• kicad-testing-small
• kicadAddons.kikit
• kicadAddons.kikit-library
• kikit
• kikit.dist
• python311Packages.diffimg
• python311Packages.diffimg.dist
• python311Packages.kicad
• python311Packages.pcbnew-transition
• python311Packages.pcbnew-transition.dist
• python311Packages.pytest-image-diff
• python311Packages.pytest-image-diff.dist
• python312Packages.diffimg
• python312Packages.diffimg.dist
• python312Packages.pytest-image-diff
• python312Packages.pytest-image-diff.dist