Bump multidict from 5.0.2 to 5.1.0 (#5308)

Bumps [multidict](https://github.com/aio-libs/multidict) from 5.0.2 to 5.1.0.
- [Release notes](https://github.com/aio-libs/multidict/releases)
- [Changelog](https://github.com/aio-libs/multidict/blob/master/CHANGES.rst)
- [Commits](aio-libs/multidict@v5.0.2...v5.1.0)

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

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

requirements/multidict.txt

@@ -1 +1 @@
-multidict==5.0.2
+multidict==5.1.0