Avoid using Cocoapods 1.15 until it fixes an issue affection RN. (#42702

)

Summary:
Cocoapods 1.15 (#42698) current breaks the build, limit to version >= 1.13 & < 1.15

This is currently broken and affecting users, we'll remove this limit once Cocopods fixes the regression.  It's currently blocking 0.73.3.
[iOS][Fixed] don't allow cocoapods 1.15.

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Pull Request resolved: #42702

Test Plan:
```
bundle exec pod install
```

Reviewed By: cipolleschi

Differential Revision: D53180111

Pulled By: blakef

fbshipit-source-id: 4c5dd11db6d208e8d71249443a8f85e601913abd

packages/rn-tester/Gemfile

@@ -1,6 +1,8 @@
 # Gemfile
 source 'https://rubygems.org'
 
-gem 'cocoapods', '>= 1.11.3'
+# Cocoapods 1.15 introduced a bug which break the build. We will remove the upper
+# bound in the template on Cocoapods with next React Native release.
+gem 'cocoapods', '>= 1.13', '< 1.15'
 gem 'rexml'
 gem 'activesupport', '>= 6.1.7.3', '< 7.1.0'