Always wrap waitpid in TEMP_FAILURE_RETRY.

Strictly not needed in the WNOHANG case, but it's probably best to have
every waitpid wrapped for future copy & pasters.

Bug: https://issuetracker.google.com/69525592
Test: ran tests
Change-Id: I013b0a52d2753e3d32638e9b84c79af7327fb405
diff --git a/tests/utils.h b/tests/utils.h
index ba006f1..9a8eb5d 100644
--- a/tests/utils.h
+++ b/tests/utils.h
@@ -140,7 +140,7 @@
 
 static inline void AssertChildExited(int pid, int expected_exit_status) {
   int status;
-  ASSERT_EQ(pid, waitpid(pid, &status, 0));
+  ASSERT_EQ(pid, TEMP_FAILURE_RETRY(waitpid(pid, &status, 0)));
   if (expected_exit_status >= 0) {
     ASSERT_TRUE(WIFEXITED(status));
     ASSERT_EQ(expected_exit_status, WEXITSTATUS(status));