[release] Also split the onlyPackages param (facebook#32777)

I missed this the last time.
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[//]: # (BEGIN SAPLING FOOTER)
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* facebook#32778
* __->__ facebook#32777

Author: poteto

scripts/release/prepare-release-from-npm-commands/parse-params.js

@@ -56,6 +56,7 @@ module.exports = () => {
   const params = commandLineArgs(paramDefinitions);
 
   splitCommaParams(params.skipPackages);
+  splitCommaParams(params.onlyPackages);
 
   return params;
 };

scripts/release/publish-commands/parse-params.js

@@ -49,6 +49,7 @@ const paramDefinitions = [
 module.exports = () => {
   const params = commandLineArgs(paramDefinitions);
   splitCommaParams(params.skipPackages);
+  splitCommaParams(params.onlyPackages);
   splitCommaParams(params.tags);
   params.tags.forEach(tag => {
     switch (tag) {