Update Ably-cocoa dependency to 1.2.6

[ben-xD]

To test Marat's changes in ably/ably-cocoa#1184 as he requested, I had to make small changes to Ably Flutter to use the latest version. It makes sense to push these changes now.

[ben-xD]

The integration tests are consistently failing, as the integration test app crashes. When running it locally, I got the following crash logs from the integration test app (not the integration test app driver):

Launching lib/main.dart on iPhone SE BB🔫 in debug mode...
Automatically signing iOS for device deployment using specified development team in Xcode project: XXY98AVDR6
Running Xcode build...
Xcode build done.                                           12.6s
Installing and launching...
(lldb) 2021-10-20 20:42:07.464367+0100 Runner[643:211894] AblyFlutterPlugin.m:556 registrar: FlutterEngineRegistrar
Debug service listening on ws://127.0.0.1:8888/ws
Syncing files to device iPhone SE BB🔫...
AblyFlutterPlugin.m:644 registerAbly()
AblyFlutterPlugin.m:644 createRestWithOptions(AblyFlutterMessage)
VERBOSE: (ARTRest.m:178) RS:0x2829e80a0 0x2818de960 alloc HTTP
DEBUG: (ARTAuth.m:156) RS:0x2829e80a0 validating <ARTClientOptions: 0x143fa9570> - 
	 key: (null); 
	 token: (null); 
	 authUrl: (null); 
	 authMethod: GET; 
	 hasAuthCallback: 1;
	 clientId: someClientId;
DEBUG: (ARTAuth.m:181) RS:0x2829e80a0 setting up auth method Token with authCallback
VERBOSE: (ARTRest.m:195) RS:0x2829e80a0 initialized
AblyFlutterPlugin.m:644 publish(AblyFlutterMessage)
DEBUG: (ARTRestChannel.m:129) RS:0x283cc0360 instantiating under 'test'
VERBOSE: RS:0x2829e80a0 ARTJsonLikeEncoder<msgpack>: messageToDictionary {
    id = "1G+ALSlho3NU:0";
}
DEBUG: RS:0x2829e80a0 ARTJsonLikeEncoder<msgpack> encoding '(
        {
        id = "1G+ALSlho3NU:0";
    }
)'; got: {length = 20, bytes = 0x9181a26964ae31472b414c536c686f334e553a30}
DEBUG: (ARTRestChannel.m:306) RS:0x2829e80a0 C:0x283cc0360 (test) post message (null)
DEBUG: (ARTRest.m:254) RS:0x2829e80a0 calculating authorization 1
VERBOSE: RS:0x2829e80a0 ARTAuthInternal [authorize.28B2CFC6-7D1E-4035-A401-B8524044C1F2, delegate=NO]: requesting new token
DEBUG: RS:0x2829e80a0 ARTAuth: using authCallback
-[NSObject toTokenDetails:callback:]: unrecognized selector sent to instance 0x281af8010
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSObject toTokenDetails:callback:]: unrecognized selector sent to instance 0x281af8010'
*** First throw call stack:
(0x194591754 0x1a90587a8 0x194494c3c 0x1945942ac 0x1945965b0 0x102976838 0x102a06cec 0x102a06bbc 0x102976d58 0x19417ca84 0x19417e81c 0x194186004 0x194186c00 0x1941914bc 0x1e016e7a4 0x1e017574c)
libc++abi: terminating with uncaught exception of type NSException
* thread #4, queue = 'io.ably.main', stop reason = signal SIGABRT
    frame #0: 0x00000001c2722334 libsystem_kernel.dylib`__pthread_kill + 8
libsystem_kernel.dylib`__pthread_kill:
->  0x1c2722334 <+8>:  b.lo   0x1c2722354               ; <+40>
    0x1c2722338 <+12>: pacibsp 
    0x1c272233c <+16>: stp    x29, x30, [sp, #-0x10]!
    0x1c2722340 <+20>: mov    x29, sp
Target 0: (Runner) stopped.
Lost connection to device.
Failed to send request: {"jsonrpc":"2.0","id":"33","method":"ext.flutter.inspector.getSelectedSummaryWidget","params":{"objectGroup":"selection_1","isolateId":"isolates/3511553721951271"}}

Now I need to figure out how to run the integration test app through Xcode whilst still allowing the driver to connect to integration test app, to potentially get more IDE help for the crash.

It seems that if the app is launched from Xcode, the test driver cannot connect to it.