ci: grant pull-requests:read so lint-pr-title workflow starts (#98)

## Summary

Adds `permissions: pull-requests: read` at the workflow level in
`.github/workflows/lint-pr-title.yml`.

The reusable workflow at
`launchdarkly/gh-actions/.github/workflows/lint-pr-title.yml@main` was
updated (in
[gh-actions#86](launchdarkly/gh-actions#86)) to
declare `permissions: pull-requests: read` at the job level. A reusable
workflow can only request a subset of the permissions the caller grants.
Without an explicit `permissions` block in the caller, the called job
fails with `startup_failure`. Same fix as
[sdk-meta#429](launchdarkly/sdk-meta#429).

## Review & Testing Checklist for Human

- [ ] Verify the `Lint PR title` workflow run on this PR exits `success`
rather than `startup_failure`

### Notes

No product code is changed — workflow-only permissions fix. Only
`pull-requests: read` is granted, matching the minimum scope the
reusable workflow requires.

Link to Devin session:
https://app.devin.ai/sessions/c7b96da5c9074500aa684bc9a9ba1c31
Requested by: @kinyoklion

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk workflow-only change that minimally expands GitHub Actions
permissions to `pull-requests: read` to avoid reusable-workflow startup
failures.
> 
> **Overview**
> Ensures the `Lint PR title` reusable workflow can start by explicitly
granting **workflow-level** `permissions: pull-requests: read` in
`.github/workflows/lint-pr-title.yml`, matching the minimum permissions
required by the called workflow and preventing `startup_failure`.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
e2c27b0. 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

@@ -7,6 +7,9 @@ on:
       - edited
       - synchronize
 
+permissions:
+  pull-requests: read
+
 jobs:
   lint-pr-title:
     uses: launchdarkly/gh-actions/.github/workflows/lint-pr-title.yml@main