Increase timing window for min duration tests to 1s

This test tends to be brittle on Mac CI machines, which are
heavily loaded and bursty. Since the tests are only run as part
of the "extra tests" test set, this increase should not have
a significant impact on the total duration of CI runs.

tests/SelfTest/TimingTests/Sleep.tests.cpp

@@ -16,8 +16,8 @@ TEST_CASE( "sleep_for_100ms", "[.min_duration_test][approvals]" )
   CHECK( true );
 }
 
-TEST_CASE( "sleep_for_250ms", "[.min_duration_test][approvals]" )
+TEST_CASE( "sleep_for_1000ms", "[.min_duration_test][approvals]" )
 {
-  std::this_thread::sleep_for( std::chrono::milliseconds( 250 ) );
+  std::this_thread::sleep_for( std::chrono::milliseconds( 1'000 ) );
   CHECK( true );
 }