Bump pysaml2 from 6.4.1 to 6.5.0 in /backend

Bumps [pysaml2](https://github.com/IdentityPython/pysaml2) from 6.4.1 to 6.5.0.
- [Release notes](https://github.com/IdentityPython/pysaml2/releases)
- [Changelog](https://github.com/IdentityPython/pysaml2/blob/master/CHANGELOG.md)
- [Commits](IdentityPython/pysaml2@v6.4.1...v6.5.0)

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

Author: dependabot[bot]

backend/requirements.txt

@@ -15,7 +15,7 @@ python-dateutil==2.8.1
 django-constance[database]==2.8.0
 drf-writable-nested==0.6.3
 git+https://github.com/magenta-aps/django-saml2-auth@2.2.6#egg=django-saml2-auth
-pysaml2==6.4.1
+pysaml2==6.5.0
 # Use latest development commit of django-mailer while we wait for
 # https://github.com/pinax/django-mailer/pull/155 to be included in a release
 git+https://github.com/pinax/django-mailer@41db3e2