ci: add pull-requests read permission to lint-pr-title workflow (#569)

## Summary

The reusable `lint-pr-title.yml` in `gh-actions` was updated (`de4859c`)
to declare `permissions: pull-requests: read` at the job level. Without
a matching top-level `permissions` block in the calling workflow,
`pull_request_target` runs hit `startup_failure`. Adds the missing
`permissions` block, matching other LD repos (e.g. `swift-eventsource`,
`go-server-sdk`).

Link to Devin session:
https://app.devin.ai/sessions/43117682510646828d0bde0908f25835
Requested by: @kinyoklion

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> CI-only workflow permission and pin update with no application or
runtime impact.
> 
> **Overview**
> Fixes **Lint PR title** failing at startup on `pull_request_target` by
adding a workflow-level **`permissions: pull-requests: read`** block,
aligned with the updated reusable workflow in `launchdarkly/gh-actions`.
> 
> The caller pin is bumped from `f1760cc` to **`de4859c`**, which
expects that permission to be declared in the calling repo.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
44a137a. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: kinyoklion

.github/workflows/lint-pr-title.yml

@@ -7,7 +7,10 @@ on:
       - edited
       - synchronize
 
+permissions:
+  pull-requests: read
+
 jobs:
   lint-pr-title:
-    # https://github.com/launchdarkly/gh-actions/commit/f1760cc538c362c2ab826a3bd22611743ef8f82c
+    # https://github.com/launchdarkly/gh-actions/commit/de4859c8d07c097d573fbcc4bd10b77efed0f5cc
     uses: launchdarkly/gh-actions/.github/workflows/lint-pr-title.yml@de4859c8d07c097d573fbcc4bd10b77efed0f5cc