chore: resolve swift lints and compiler warnings

[vaind]

#skip-changelog

closes #867

resolves the following compiler warnings:

/flutter/ios/Classes/SentryFlutterPluginApple.swift:470:35: warning: expression implicitly coerced from 'Dictionary<String, Any?>' to '[String : Any]'
          scope.setContext(value: dictionary, key: key)
                                  ^~~~~~~~~~
          scope.setContext(value: dictionary, key: key)
                                  ^~~~~~~~~~
                                             as [String : Any]
/flutter/ios/Classes/SentryFlutterPluginApple.swift:472:45: warning: expression implicitly coerced from 'String?' to 'Any'
          scope.setContext(value: ["value": string], key: key)
                                            ^~~~~~
          scope.setContext(value: ["value": string], key: key)
                                            ^~~~~~
                                                   ?? <#default value#>
          scope.setContext(value: ["value": string], key: key)
                                            ^~~~~~
                                                  !
          scope.setContext(value: ["value": string], key: key)
                                            ^~~~~~
                                                   as Any
/flutter/ios/Classes/SentryFlutterPluginApple.swift:512:31: warning: expression implicitly coerced from 'Dictionary<String, Any?>' to '[String : Any]'
          userInstance.data = extras
                              ^~~~~~
          userInstance.data = extras
                              ^~~~~~
                                     as [String : Any]
/flutter/ios/Classes/SentryFlutterPluginApple.swift:557:35: warning: expression implicitly coerced from 'Dictionary<String, Any?>' to '[String : Any]'
        breadcrumbInstance.data = data
                                  ^~~~
        breadcrumbInstance.data = data
                                  ^~~~
                                       as [String : Any]

and the lints from the CI

[marandaneto]

Fixes #867