os: freeze signals constant

Remove the ability to mutate signals constant as doing so can lead to
unexpected behavior, notably when spawning child process.

Fixes: #44749

Author: Xstoudi

lib/os.js

@@ -27,6 +27,7 @@ const {
   ObjectDefineProperties,
   StringPrototypeSlice,
   SymbolToPrimitive,
+  ObjectFreeze,
 } = primordials;
 
 const { getTempDir } = internalBinding('credentials');
@@ -330,6 +331,8 @@ module.exports = {
   machine: getMachine,
 };
 
+ObjectFreeze(constants.signals);
+
 ObjectDefineProperties(module.exports, {
   constants: {
     __proto__: null,