chore: only lint changed READMEs

Update changed-files library to grab a fix to the glob library that was
outputing all changed files if no file matched the pattern.

.github/workflows/readme-linter.yml

@@ -15,9 +15,10 @@ jobs:
           fetch-depth: 0
       - name: Get changed files
         id: changed-files
-        uses: tj-actions/changed-files@v18.7
+        uses: tj-actions/changed-files@v26.1
         with:
           base_sha: ${{ github.event.pull_request.base.sha }}
-          files: plugins/**/README.md
+          files: ./plugins/**/README.md
       - name: Run readme linter on changed files
+        if: steps.changed-files.outputs.any_changed == 'true'
         run: go run ./tools/readme_linter ${{ steps.changed-files.outputs.all_changed_files }}