terminate the XCUIApplication as part of UI tests setUpTestSuite

Co-authored-by: pachlava <pachlava@gmail.com>

This is an attempt to address UI tests flakiness.

See #17886 for
more details.

Author: mokagio

WordPress/WordPressUITests/Utils/XCTest+Extensions.swift

@@ -10,6 +10,7 @@ extension XCTestCase {
         continueAfterFailure = false
 
         let app = XCUIApplication()
+        app.terminate()
         app.launchArguments = ["-wpcom-api-base-url", WireMock.URL().absoluteString, "-no-animations", "-ui-testing"]
         app.activate()