elixir-ls: fix building with elixir_1_16

[adamcstephens]

Description of changes

Fixes error when building with elixir 1.16

error: builder for '/nix/store/4bk3i1cyf6a6dxm9j31j9z4wf860iw3r-elixir-ls-0.20.0.drv' failed with exit code 1;
       last 10 log lines:
       >
       > ** (UndefinedFunctionError) function Mix.Dep.load_on_environment/1 is undefined or private

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.

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[happysalada]

Oh wow thats amazing, this is the last thing before the global elixir switch can be set to 1.16

Ill try to test that soon