fix cp command in ReactNativeDependencies.podspec (#53136)

Summary:
When running `RCT_USE_PREBUILT_RNCORE=1 RCT_USE_RN_DEP=1 pod install` I'm getting an error: `cp: framework/packages/react-native/..: File exists`

This is not seen consistently by everyone but I've seen in reported one more time at Expo. Could be related to running MacOS 26.

Somehow, apparently, the `..` is being treated as a literal directory name and cp is trying to create a directory named `..` inside `framework/packages/react-native/` which is not what we want. Using `/.` avoids that.

 ---
What also seemed to work(around) was to change `mkdir -p framework/packages/react-native` to `mkdir -p framework/packages/` and then `cp` can create the `framework/packages/react-native/..` folder. But this is definitely more confusing.

## Changelog:

Pick one each for the category and type tags:

[IOS] [FIXED] - fix "file exists" error in `ReactNativeDependencies.podspec`

Pull Request resolved: https://github.com/facebook/react-native/pull/53136

Test Plan: tested locally, and in CI on older macOS: https://github.com/expo/expo/pull/38631 (the ios build succeeds)

Reviewed By: rshest

Differential Revision: D79990895

Pulled By: cipolleschi

fbshipit-source-id: 44ff9034800d3acd4e55ec39aabfb326382372cb

packages/react-native/third-party-podspecs/ReactNativeDependencies.podspec

@@ -64,7 +64,7 @@ Pod::Spec.new do |spec|
 
     cp -R "$HEADERS_PATH/" Headers
     mkdir -p framework/packages/react-native
-    cp -R "$XCFRAMEWORK_PATH/.." framework/packages/react-native/
+    cp -R "$XCFRAMEWORK_PATH/../." framework/packages/react-native/
     find "$XCFRAMEWORK_PATH/.." -type f -exec rm {} +
     find "$CURRENT_PATH" -type d -empty -delete
   CMD