Bump ansible-core from 2.15.6 to 2.15.7 in /requirements/v2.15

Bumps [ansible-core](https://github.com/ansible/ansible) from 2.15.6 to 2.15.7.
- [Release notes](https://github.com/ansible/ansible/releases)
- [Commits](ansible/ansible@v2.15.6...v2.15.7)

---
updated-dependencies:
- dependency-name: ansible-core
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

requirements/v2.15/requirements.txt

@@ -1 +1 @@
-ansible-core==2.15.6
+ansible-core==2.15.7