fix(ios): skip script phases on abstract targets

[Salakar]

Summary:

Abstract targets don't support script phases, this change skips adding script phases if the current target is abstract.

Fixes invertase/react-native-firebase#2800

cc @orta / @alloy for review please, thanks!

Test Plan:

@gabrielbull would you be able to patch package this change in and confirm it now works? invertase/react-native-firebase#2800

---

script phases continue to work on non abstract targets:

[grabbou]

Looks good to me. Going to wait for one more review before moving forward. Thanks for sending over the PR.

[alloy]

Yup, this looks good to me 👍

[thymikee]

Thanks @alloy, @Salakar! This is released in v3.2.

[r0ssIV]

@Salakar @thymikee hello, what about real targets inside abstract targets ? Pls also check link above.

abstract_target 'SomeAbstractTarget' do
  config = use_native_modules!

 .... abbreviated for example....

  target 'RealTarget' do
    # Production-specific pods

    target 'RealTargetTests' do
      inherit! :complete
      # Pods for testing
    end
  end

end