feat(react-native-sdk): update podspec file

react-native-sdk/jitsi-meet-rnsdk.podspec

   s.source         = { :git => package['repository']['url'], :tag => s.version }
 
   s.requires_arc   = true
-  s.platform       = :ios, '12.4'
+  s.platform       = :ios, '15.1'
 
   s.preserve_paths = 'ios/**/*'
   s.source_files   =  'ios/**/*.{h,m}'