Update requests requirement from ~=2.27.1 to ~=2.28.1 in /api

Updates the requirements on [requests](https://github.com/psf/requests) to permit the latest version.
- [Release notes](https://github.com/psf/requests/releases)
- [Changelog](https://github.com/psf/requests/blob/main/HISTORY.md)
- [Commits](https://github.com/psf/requests/compare/v2.27.1...v2.28.1)

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

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

api/requirements.txt

@@ -12,7 +12,7 @@ pytest~=7.1.2
 pytest-cov
 marshmallow~=3.15.0
 faker~=13.11.0
-requests~=2.27.1
+requests~=2.28.1
 investpy~=1.0.8
 pandas~=1.4.2
 currencyconverter~=0.16.12