Bump dorny/paths-filter from 3 to 4

Bumps [dorny/paths-filter](https://github.com/dorny/paths-filter) from 3 to 4.
- [Release notes](https://github.com/dorny/paths-filter/releases)
- [Changelog](https://github.com/dorny/paths-filter/blob/master/CHANGELOG.md)
- [Commits](dorny/paths-filter@v3...v4)

---
updated-dependencies:
- dependency-name: dorny/paths-filter
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/backend.yml

@@ -27,7 +27,7 @@ jobs:
   changes:
     # Path filtering only gates pull_request events; pushes to protected
     # branches always run downstream regardless of which files changed.
-    # dorny/paths-filter@v3 additionally needs a checked-out repo on push
+    # dorny/paths-filter@v4 additionally needs a checked-out repo on push
     # events (it shells out to `git branch --show-current`), so scoping
     # this job to pull_request avoids the "fatal: not a git repository"
     # red X that would otherwise appear on every push to main.
@@ -42,9 +42,9 @@ jobs:
     outputs:
       backend: ${{ steps.filter.outputs.backend }}
     steps:
-      # No checkout needed: dorny/paths-filter@v3 reads diffs from the
+      # No checkout needed: dorny/paths-filter@v4 reads diffs from the
       # pull_request event payload.
-      - uses: dorny/paths-filter@v3
+      - uses: dorny/paths-filter@v4
         id: filter
         with:
           filters: |