Bump scipy from 1.6.3 to 1.7.1 in /requirements/CI-tests-pip

Bumps [scipy](https://github.com/scipy/scipy) from 1.6.3 to 1.7.1.
- [Release notes](https://github.com/scipy/scipy/releases)
- [Commits](scipy/scipy@v1.6.3...v1.7.1)

---
updated-dependencies:
- dependency-name: scipy
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements/CI-tests-pip/requirements.txt

@@ -7,5 +7,5 @@ numpy==1.21.0
 pytest==6.2.4
 pytest-xdist==2.3.0
 python_jsonschema_objects==0.4.0
-scipy==1.6.3
+scipy==1.7.1
 tskit==0.3.6