chore: add t-tooling label to new PRs as well (#1116)

Extends the new-issue labeling workflow to also run on PR open, adding
the `t-tooling` label. Replicates apify/crawlee#4222.

- Uses `pull_request_target` so the token can write labels on PRs from
forks (nothing is checked out, so this is safe).
- Adds `pull-requests: write` permission. `context.issue.number` already
resolves to the PR number for PR events.

[🤖] Claude Code using Opus 5.5

Author: vladfrangu

.github/workflows/on_issue.yaml

@@ -1,10 +1,14 @@
-name: CI (issue)
+name: CI (issue or PR)
 
 on:
   # Runs when a new issue is opened.
   issues:
     types:
       - opened
+  # Runs when a new PR is opened. pull_request_target so the token has write access for PRs from forks; no code is checked out here.
+  pull_request_target:
+    types:
+      - opened
 
 permissions:
   contents: read
@@ -15,9 +19,10 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       issues: write
+      pull-requests: write
 
     steps:
-      # Add the "t-tooling" label to all new issues
+      # Add the "t-tooling" label to all new issues and PRs
       - uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
         with:
           script: |