test: fix determining lower priority

PR-URL: #55908Fixes: NixOS/nixpkgs#355919
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: LiviaMedeiros

test/parallel/test-os.js

@@ -84,7 +84,8 @@ assert.ok(hostname.length > 0);
 // IBMi process priority is different.
 if(!common.isIBMi){
 const{PRIORITY_BELOW_NORMAL,PRIORITY_LOW}=os.constants.priority;
-constLOWER_PRIORITY=os.getPriority()>PRIORITY_BELOW_NORMAL ? PRIORITY_BELOW_NORMAL : PRIORITY_LOW;
+// Priority means niceness: higher numeric value <=> lower priority
+constLOWER_PRIORITY=os.getPriority()<PRIORITY_BELOW_NORMAL ? PRIORITY_BELOW_NORMAL : PRIORITY_LOW;
 os.setPriority(LOWER_PRIORITY);
 constpriority=os.getPriority();
 is.number(priority);