Reduce the warm up and measurement time for short-benchmarks

The icount benchmarks are what we will be relying on in CI more than the
existing benchmarks. There isn't much reason to keep these around, but
there isn't much point in dropping them either. So, just reduce the
runtime.

Author: tgross35

crates/libm-test/benches/random.rs

@@ -151,8 +151,8 @@ pub fn musl_random() {
     // about the same time as other tests.
     if cfg!(feature = "short-benchmarks") {
         criterion = criterion
-            .warm_up_time(Duration::from_millis(500))
-            .measurement_time(Duration::from_millis(1000));
+            .warm_up_time(Duration::from_millis(200))
+            .measurement_time(Duration::from_millis(600));
     }
 
     criterion = criterion.configure_from_args();