Bump pytest-asyncio in /testing/plugins_integration

Bumps [pytest-asyncio](https://github.com/pytest-dev/pytest-asyncio) from 0.14.0 to 0.15.0.
- [Release notes](https://github.com/pytest-dev/pytest-asyncio/releases)
- [Commits](pytest-dev/pytest-asyncio@v0.14.0...v0.15.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

testing/plugins_integration/requirements.txt

@@ -1,6 +1,6 @@
 anyio[curio,trio]==2.2.0
 django==3.2
-pytest-asyncio==0.14.0
+pytest-asyncio==0.15.0
 pytest-bdd==4.0.2
 pytest-cov==2.11.1
 pytest-django==4.2.0