Bump msal from 1.26.0 to 1.28.0 in /backend/requirements (#1626)

Bumps [msal](https://github.com/AzureAD/microsoft-authentication-library-for-python) from 1.26.0 to 1.28.0.
- [Release notes](https://github.com/AzureAD/microsoft-authentication-library-for-python/releases)
- [Commits](AzureAD/microsoft-authentication-library-for-python@1.26.0...1.28.0)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

backend/requirements/default.txt

@@ -32,7 +32,7 @@ langchain-text-splitters==0.0.1
 litellm==1.43.18
 llama-index==0.9.45
 Mako==1.2.4
-msal==1.26.0
+msal==1.28.0
 nltk==3.8.1
 Office365-REST-Python-Client==2.5.9
 oauthlib==3.2.2