Update the sourceproperty to avoid multiple downloads (facebook#54031)

Summary:
Pull Request resolved: facebook#54031

This commit updates the cocoapods source for RNDependencies so that the source for the package is the locally downloaded file so we don't download twice!

## Changelog:

[IOS] [FIXED] - Update the `source`property to avoid multiple downloads

Test Plan:
Run:
```
RCT_USE_RN_DEP=1 RCT_USE_PREBUILT_RNCORE=1 bundle exec pod install
```

Multiple times and observe that the dependencies are not downloaded multiple times.

Reviewed By: christophpurrer

Differential Revision: D83753188

Pulled By: cipolleschi

fbshipit-source-id: e3fedca921b0ff9ba10ec3e5a7ba18dfbdffc3ba

Author: chrfalch

packages/react-native/scripts/cocoapods/rndependencies.rb

@@ -158,9 +158,10 @@ def self.podspec_source_download_prebuild_release_tarball()
 
         url = release_tarball_url(@@react_native_version, :debug)
         rndeps_log("Using tarball from URL: #{url}")
-        download_stable_rndeps(@@react_native_path, @@react_native_version, :debug)
+        destinationDebug = download_stable_rndeps(@@react_native_path, @@react_native_version, :debug)
         download_stable_rndeps(@@react_native_path, @@react_native_version, :release)
-        return {:http => url}
+
+        return {:http => URI::File.build(path: destinationDebug).to_s }
     end
 
     def self.release_tarball_url(version, build_type)