Update dependency RxRelay to ~> 6.8.0

| datasource | package | from  | to    |
| ---------- | ------- | ----- | ----- |
| pod        | RxRelay | 6.7.1 | 6.8.0 |

Author: renovate[bot]

sample/iosApp/Podfile

@@ -14,7 +14,7 @@ target 'iosApp-RxSwift' do
   pod 'Kingfisher', '~> 8.0.0'
   pod 'RxSwift', '~> 6.7.0'
   pod 'RxCocoa', '~> 6.7.0'
-  pod 'RxRelay', '~> 6.7.0'
+  pod 'RxRelay', '~> 6.8.0'
   pod 'NSObject+Rx', '~> 5.2.2'
   pod 'RxDataSources', '~> 5.0'
   pod 'MBProgressHUD', '~> 1.2.0'