Update marshmallow requirement from ~=3.15.0 to ~=3.18.0 in /api

Updates the requirements on [marshmallow](https://github.com/marshmallow-code/marshmallow) to permit the latest version.
- [Release notes](https://github.com/marshmallow-code/marshmallow/releases)
- [Changelog](https://github.com/marshmallow-code/marshmallow/blob/dev/CHANGELOG.rst)
- [Commits](https://github.com/marshmallow-code/marshmallow/compare/3.15.0...3.18.0)

---
updated-dependencies:
- dependency-name: marshmallow
  dependency-type: direct:production
...

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

api/requirements.txt

@@ -10,7 +10,7 @@ flask-cors==3.0.10
 bcrypt==3.2.2
 pytest~=7.1.2
 pytest-cov
-marshmallow~=3.15.0
+marshmallow~=3.18.0
 faker~=13.11.0
 requests~=2.27.1
 investpy~=1.0.8