tools: fix small not-quite-a-bug in find-inactive-tsc.mjs

The current code attempts to count votes from people who were not
members at the start of the 3 month period, resulting in `NaN` being
tallied for their votes.

PR-URL: https://github.com/nodejs/node/pull/41469
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Tierney Cyren <hello@bnb.im>

tools/find-inactive-tsc.mjs

@@ -118,7 +118,9 @@ async function getVotingRecords(tscMembers, votes) {
       await fs.promises.readFile(path.join('.tmp', vote), 'utf8')
     );
     for (const member in voteData.votes) {
-      votingRecords[member]++;
+      if (tscMembers.includes(member)) {
+        votingRecords[member]++;
+      }
     }
   }
   return votingRecords;