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

@@ -18,7 +18,7 @@ python-dateutil==2.8.1
 django-constance[database]==2.8.0
 drf-writable-nested==0.6.2
 git+https://github.com/magenta-aps/django-saml2-auth@2.2.6#egg=django-saml2-auth
-pysaml2==6.4.1
+pysaml2==6.5.0
 django-mailer==2.1
 holidays==0.10.4
 django-watchman==1.2.0