`APIManagerTests.testConcurrentRequests` fails on Linux

```
Test Case 'APIManagerTests.testConcurrentRequests' started at 2024-11-18 18:43:27.208
/home/runner/work/flagsmith-ios-client/flagsmith-ios-client/FlagsmithClient/Tests/APIManagerTests.swift:83: error: APIManagerTests.testConcurrentRequests : Asynchronous wait failed - Exceeded timeout of 10.0 seconds, with unfulfilled expectations: Multiple threads can access the APIManager 310, Multiple threads can access the APIManager 321, Multiple threads can access the APIManager 329, Multiple threads can access the APIManager 378, Multiple threads can access the APIManager 393, Multiple threads can access the APIManager 399, Multiple threads can access the APIManager 428, Multiple threads can access the APIManager 458, Multiple threads can access the APIManager 459, Multiple threads can access the APIManager 463, Multiple threads can access the APIManager 465, Multiple threads can access the APIManager 466, Multiple threads can access the APIManager 468, Multiple threads can access the APIManager 469, Multiple threads can access the APIManager 473, Multiple threads can access the APIManager 475, Multiple threads can access the APIManager 477, Multiple threads can access the APIManager 478, Multiple threads can access the APIManager 484, Multiple threads can access the APIManager 490, Multiple threads can access the APIManager 492, Multiple threads can access the APIManager 495, Multiple threads can access the APIManager 497, Multiple threads can access the APIManager 498, Multiple threads can access the APIManager 499
```

Start by running APIManagerTests.testConcurrentRequests on Linux and inspect the failure at FlagsmithClient/Tests/APIManagerTests.swift:83. Trace the concurrent APIManager requests and determine why the expectations remain unfulfilled; done means the test completes successfully on Linux without exceeding its timeout.

Written by the indexing model from the issue text.