[Snyk] Security upgrade django from 3.2.14 to 3.2.15 (#84)

fix: cvat/requirements/base.txt to reduce vulnerabilities


The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-2968205

Co-authored-by: snyk-bot <snyk-bot@snyk.io>

cvat/requirements/base.txt

@@ -1,6 +1,6 @@
 attrs==21.4.0
 click==7.1.2
-Django==3.2.14
+Django==3.2.15
 django-appconf==1.0.4
 django-auth-ldap==2.2.0
 django-compressor==2.4