Remove one more unnecessary type boundary

Author: dkhalanskyjb

kotlinx-coroutines-core/common/test/AtomicCancellationCommonTest.kt

@@ -138,7 +138,7 @@ class AtomicCancellationCommonTest : TestBase() {
         val mutex = Mutex(true) // locked mutex
         val job = launch(start = CoroutineStart.UNDISPATCHED) {
             expect(2)
-            select<String> { // suspends
+            select { // suspends
                 mutex.onLock {
                     expect(4)
                     "OK"
@@ -152,4 +152,4 @@ class AtomicCancellationCommonTest : TestBase() {
         yield() // now yield
         finish(4)
     }
-}
+}