Export *just* the AppDistributionInternal source code to master to fix CI issues

[tejasd]

There are CI failures which seem to need this source code in master.

Eg. https://github.com/firebase/firebase-ios-sdk/actions/runs/4387975314/jobs/7683918159

This PR is an attempt at that.

#no-changelog

[paulb777]

I believe two other alternatives to this would be pushing AppDistribution-internal to SpecsDev or temporarily disabling the failing CI job in your branch.

[tejasd]

Pushing it to SpecsDev errors out - which occurs because it's not possible to specify a branch besides master in the podspec AFAICT.

Validating spec
 -> FirebaseAppDistributionInternal (10.5.0-beta)
    - ERROR | [iOS] file patterns: The `source_files` pattern did not match any file.
    - ERROR | [iOS] file patterns: The `resource_bundles` pattern for `AppDistributionInternalResources` did not match any file.
    - ERROR | [iOS] unknown: Encountered an unknown error (Unable to install the `FirebaseAppDistributionInternal` pod, because the `FirebaseAppDistributionInternal-Unit-unit` target in Xcode would have no sources to compile.) during validation.

It's possible to temporarily disable the CI tasks - but this seems like a harmless change (it won't be included in spm, it's not added as a dependency to FirebaseAppDistribution.

The only thing I'm not sure if anything is needed, is to prevent it from being pushed to https://cdn.cocoapods.org/ from master?

[paulb777]

I see. You'd need to change the podspec to successfully push to SpecsDev.

I agree it should be safe to do it this other way. We won't try to publish until it gets added to FirebaseManifest.swift