python3Packages.mat2: fix tests against ffmpeg 4.4

[risicle]

Motivation for this change

ZHF #122042

Seems upstream have already noticed this breakage and have fixed it in master.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Added a release notes entry if the change is major or breaking
• Fits CONTRIBUTING.md.

[r-rmcgibbo]

Result of nixpkgs-review pr 124552 at 6d8b59a run on aarch64-linux 1

3 packages built successfully:

• mat2 (python38Packages.mat2)
• metadata-cleaner
• python39Packages.mat2

---

Result of nixpkgs-review pr 124552 at 6d8b59a run on x86_64-linux 1

3 packages built successfully:

• mat2 (python38Packages.mat2)
• metadata-cleaner
• python39Packages.mat2

[veprbl]

@GrahamcOfBorg build mat2 metadata-cleaner python38Packages.mat2 python39Packages.mat2