Bump sphinxcontrib-spelling from 7.0.1 to 7.1.0 (aio-libs#5206)

Bumps [sphinxcontrib-spelling](https://github.com/sphinx-contrib/spelling) from 7.0.1 to 7.1.0.
- [Release notes](https://github.com/sphinx-contrib/spelling/releases)
- [Commits](sphinx-contrib/spelling@7.0.1...7.1.0)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/doc-spelling.txt

@@ -1,2 +1,2 @@
 -r doc.txt
-sphinxcontrib-spelling==7.0.1; platform_system!="Windows"  # We only use it in Travis CI
+sphinxcontrib-spelling==7.1.0; platform_system!="Windows"  # We only use it in Travis CI