ci: grant pull-requests:read so lint-pr-title workflow starts (#45)

## 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 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, so without an
explicit `permissions` block in the caller, the workflow fails with
`startup_failure`. Same fix as 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 being applied
across SDK repos that use the reusable `lint-pr-title` workflow.

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

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: workflow-only permission change to allow the reusable
`lint-pr-title` workflow to start; no product code or runtime behavior
is affected.
> 
> **Overview**
> Ensures the `Lint PR title` GitHub Actions workflow can run by
explicitly granting `permissions: pull-requests: read` at the workflow
level when invoking the reusable `launchdarkly/gh-actions` workflow.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
a45b9df. 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