chore(ci): get pr number and sha from github context (#35405)

### Issue # (if applicable)

Related to #35268 as the previous fix didn't fully work


### Reason for this change

The Pr linter workflow does not reach the code of the linter itself because it stop on error when being triggered at the end of a build, see the [following run](https://github.com/aws/aws-cdk/actions/runs/17435099055/job/49502649374) for example.

### Description of changes
Continue if `'Download workflow_run artifact'` to get the PR number and the pr sha from the Github context.


### Description of how you validated changes

Ran on my fork of the repo (canceling the build workflow retriggers this one), see the following run for example: https://github.com/leonmk-aws/aws-cdk/actions/runs/17435786087/job/49505111010

### Checklist
- [X] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: leonmk-aws

.github/workflows/pr-linter.yml

@@ -34,6 +34,7 @@ jobs:
       - name: 'Download workflow_run artifact'
         if: github.event_name == 'workflow_run'
         uses: dawidd6/action-download-artifact@v11
+        continue-on-error: true
         with:
           run_id: ${{ github.event.workflow_run.id }}
           name: pr_info
@@ -46,10 +47,10 @@ jobs:
         id: 'pr_output'
         run: |
           if [[ ! -f pr/pr_number ]]; then
-            echo "${{ github.event.pull_request.number }}" > pr/pr_number
+            echo "${{ github.event.workflow_run.pull_requests[0].number }}" > pr/pr_number
           fi
           if [[ ! -f pr/pr_sha ]]; then
-            echo "${{ github.event.pull_request.head.sha }}" > pr/pr_sha
+            echo "${{ github.event.workflow_run.head_sha }}" > pr/pr_sha
           fi
           cat pr/*
           echo "pr_number=$(cat pr/pr_number)" >> "$GITHUB_OUTPUT"