feishin: Bump electron from 36 to 38

[Daste745]

Feishin will be using electron 38 in version 0.21.3, which is currently in beta:
jeffvli/feishin@5892088

While we're still on 0.21.2, bumping electron doesn't break the app and it still works as expected.

Also resolves a warning about Electron versions below 37.0.0 being EOL.

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

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[Daste745]

I'm not sure how this kind of version bumps are handled in nixpkgs, because electron 38 isn't yet used in upstream stable builds.

Simply bumping from 36 to 38 doesn't break the build and Feishin seems to be working correctly on my machine.

Please let me known if this should be done after Feishin stable is on 0.21.3 or if this can be merged before that.