fix: cvat/requirements/base.txt to reduce vulnerabilities (#3384)

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-1315688

cvat/requirements/base.txt

 click==7.1.2
-Django==3.1.12
+Django==3.1.13
 django-appconf==1.0.4
 django-auth-ldap==2.2.0
 django-cacheops==5.0.1