chore(deps): update xa11y requirement from >=0.11.0 to >=0.13.0 (#516)

Updates the requirements on [xa11y](https://github.com/xa11y/xa11y) to permit the latest version.
- [Release notes](https://github.com/xa11y/xa11y/releases)
- [Changelog](https://github.com/xa11y/xa11y/blob/main/release.toml)
- [Commits](xa11y/xa11y@v0.11.0...v0.13.0)

---
updated-dependencies:
- dependency-name: xa11y
  dependency-version: 0.13.0
  dependency-type: direct:production
...

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Author: dependabot[bot]

requirements-testing.txt

@@ -16,4 +16,4 @@ fonttools >= 4.0.0
 deadline-cloud-test-fixtures >= 0.18.17
 # Drives the real submitter dialog via the OS accessibility tree.
 # Used by test/integ/.
-xa11y >= 0.11.0
+xa11y >= 0.13.0