process,doc: add missing deprecation code

Refs: nodejs#36902

Author: cjihrig

doc/api/deprecations.md

@@ -2711,7 +2711,7 @@ Type: Documentation-only.
 
 Prefer [`message.socket`][] over [`message.connection`][].
 
-### DEP0XXX: Changing the value of `process.config`
+### DEP0150: Changing the value of `process.config`
 <!-- YAML
 changes:
   - version: REPLACEME

lib/internal/bootstrap/node.js

@@ -72,7 +72,7 @@ const deprecationHandler = {
   warned: false,
   message: 'Setting process.config is deprecated. ' +
            'In the future the property will be read-only.',
-  code: 'DEP0XXX',
+  code: 'DEP0150',
   maybeWarn() {
     if (!this.warned) {
       process.emitWarning(this.message, {