test: fix conversion of microseconds in test

Fixes: #8728

test/pummel/test-process-cpuUsage.js

@@ -17,14 +17,14 @@ while (Date.now() - now < RUN_FOR_MS);
 // Get a diff reading from when we started.
 const diff = process.cpuUsage(start);
 
-const MICROSECONDS_PER_SECOND = 1000 * 1000;
+const MICROSECONDS_PER_MILLISECOND = 1000;
 
 // Diff usages should be >= 0, <= ~RUN_FOR_MS millis.
 // Let's be generous with the slop factor, defined above, in case other things
 // are happening on this CPU. The <= check may be invalid if the node process
 // is making use of multiple CPUs, in which case, just remove it.
 assert(diff.user >= 0);
-assert(diff.user <= SLOP_FACTOR * RUN_FOR_MS * MICROSECONDS_PER_SECOND);
+assert(diff.user <= SLOP_FACTOR * RUN_FOR_MS * MICROSECONDS_PER_MILLISECOND);
 
 assert(diff.system >= 0);
-assert(diff.system <= SLOP_FACTOR * RUN_FOR_MS * MICROSECONDS_PER_SECOND);
+assert(diff.system <= SLOP_FACTOR * RUN_FOR_MS * MICROSECONDS_PER_MILLISECOND);