Change CMAKE_OSX_DEPLOYMENT_TARGET on iOS from 8.0 to 9.0

This is due to FFmpeg v5.1.6 update:

src/libavfilter/vf_yadif_videotoolbox.m:255:17: error: 'MTLResourceStorageModeShared' is only available on iOS 9.0 or newer [-Werror,-Wunguarded-availability]
        options:MTLResourceStorageModeShared];

Library/TeamTalkLib/CMakeLists.txt

@@ -59,7 +59,7 @@ if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
 elseif (${CMAKE_SYSTEM_NAME} MATCHES "iOS")
 
   if (NOT CMAKE_OSX_DEPLOYMENT_TARGET)
-    set (CMAKE_OSX_DEPLOYMENT_TARGET 8.0)
+    set (CMAKE_OSX_DEPLOYMENT_TARGET 9.0)
     message(WARNING "No deployment target specified. Defaulting to ${CMAKE_OSX_DEPLOYMENT_TARGET}")
   endif()
   list (APPEND COMPILE_FLAGS -fembed-bitcode)