tests: have defaultClient/HTTPBin for less repetition

Author: weissi

Diff for: Tests/AsyncHTTPClientTests/HTTPClientTests+XCTest.swift

@@ -99,6 +99,7 @@ extension HTTPClientTests {
             ("testValidationErrorsAreSurfaced", testValidationErrorsAreSurfaced),
             ("testUploadsReallyStream", testUploadsReallyStream),
             ("testUploadStreamingCallinToleratedFromOtsideEL", testUploadStreamingCallinToleratedFromOtsideEL),
+            ("testUploadStreamingIsCalledOnTaskEL", testUploadStreamingIsCalledOnTaskEL),
         ]
     }
 }