[libc][NFC] Fix Implicit Conversion Warning in getrandom Test

getrandom returns a ssize_t, but the error codes are defined as
integers. We need to use the builtin cast in the Fails matcher to ensure
that everything is the same type.

clang will warn about this in a bootstrapping build. Originally found in
\#155627.

Author: boomanaiden154

libc/test/src/sys/random/linux/getrandom_test.cpp

@@ -19,11 +19,12 @@ using LlvmLibcGetRandomTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
 TEST_F(LlvmLibcGetRandomTest, InvalidFlag) {
   LIBC_NAMESPACE::cpp::array<char, 10> buffer;
   ASSERT_THAT(LIBC_NAMESPACE::getrandom(buffer.data(), buffer.size(), -1),
-              Fails(EINVAL));
+              Fails<ssize_t>(EINVAL));
 }
 
 TEST_F(LlvmLibcGetRandomTest, InvalidBuffer) {
-  ASSERT_THAT(LIBC_NAMESPACE::getrandom(nullptr, 65536, 0), Fails(EFAULT));
+  ASSERT_THAT(LIBC_NAMESPACE::getrandom(nullptr, 65536, 0),
+              Fails<ssize_t>(EFAULT));
 }
 
 TEST_F(LlvmLibcGetRandomTest, ReturnsSize) {