Allows labeler action to add/remove labels from the PR title/body on sync (#92553)

## About The Pull Request

Followup to https://github.com/tgstation/tgstation/pull/92504

Removes the conditional that was stopping the labeler from checking the
PR body for labels on sync.

<details><summary>No more of this weirdness</summary>

<img width="877" height="488" alt="firefox_zppJmK5qz2"
src="https://github.com/user-attachments/assets/74a556b5-a3e3-40e7-93dd-e18c62ed9649"
/>

</details>

Any time someone updates a PR and it syncs, you can potentially lose
some of the PR labels from the body (the changelog specifically) if they
are not configured as `add_only` in the autoLabelConfig.js

I had kept it in previously since it was how it was before, but thinking
on it I do not think this is even necessary anymore now that the php
webhook method is replaced with the action. Let's remove it!

## Why It's Good For The Game

QoL for maintainers and contributors

## Changelog

Nothing player-facing

tools/pull_request_hooks/autoLabel.js

@@ -173,7 +173,7 @@ async function check_diff_files_for_labels(github, context) {
  * Main function to get the updated label set
  */
 export async function get_updated_label_set({ github, context }) {
-  const { action, pull_request } = context.payload;
+  const { pull_request } = context.payload;
   const {
     body = "",
     diff_url,
@@ -192,14 +192,38 @@ export async function get_updated_label_set({ github, context }) {
     labels_to_remove.forEach((label) => updated_labels.delete(label));
   }
 
-  // Check body/title only when PR is opened, not on sync
-  if (action === "opened") {
-    if (title)
-      check_title_for_labels(title).forEach((label) =>
-        updated_labels.add(label)
-      );
-    if (body)
-      check_body_for_labels(body).forEach((label) => updated_labels.add(label));
+  // Always check body/title (otherwise we can lose the changelog labels)
+  if (title)
+    check_title_for_labels(title).forEach((label) =>
+      updated_labels.add(label)
+    );
+  if (body)
+    check_body_for_labels(body).forEach((label) => updated_labels.add(label));
+
+  // Keep track of labels that were manually added by maintainers in the events.
+  // And make sure they -stay- added.
+  try {
+    await github.paginate(
+      github.rest.issues.listEventsForTimeline,
+      {
+        owner: context.repo.owner,
+        repo: context.repo.repo,
+        issue_number: context.payload.pull_request.number,
+        per_page: 100,
+      },
+      (response) => {
+        for (const eventData of response.data) {
+          if (
+            eventData.event === "labeled" &&
+            eventData.actor?.login !== "github-actions"
+          ) {
+            updated_labels.add(eventData.label.name);
+          }
+        }
+      }
+    );
+  } catch (error) {
+    console.error("Error fetching paginated events:", error);
   }
 
   // Always remove Test Merge Candidate