fix: cvat/requirements/base.txt to reduce vulnerabilities (#3970)

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-PYTHONLDAP-1932572

cvat/requirements/base.txt

@@ -8,7 +8,7 @@ django-rq==2.3.2
 EasyProcess==0.3
 Pillow==8.3.2
 numpy==1.19.5
-python-ldap==3.3.1
+python-ldap==3.4.0
 pytz==2020.1
 pyunpack==0.2.1
 rcssmin==1.0.6