etesync-dav: pull patch into flask to work with setuptools 67.5.0+

[tjni]

Description of changes

Pull a patch into version 2.0.3 of flask that replaces usages of pkg_resources. In setuptools 67.5.0+, this starts to output a deprecation warning, which fails flask's tests. While we could stop running tests or patch how it responds to warnings, I thought we could use the patch to improve the behavior without changing the testing.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• 23.11 Release Notes (or backporting 23.05 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.

[natsukium]

IMO it would be better to version up instead of the patch since upstream does not pin the flask version.
https://github.com/etesync/etesync-dav/blob/cff246c13b613755fd3b709ab3318d3ddcdd9123/setup.py#L115

I would like to hear from the package maintainers, @thyol and @Valodim.

[tjni]

I do think unpinning flask is a good idea, and I am going to see if that's possible. In the meantime, I think it's best to merge this into staging-next so that the build doesn't break for users.